FTB 09-27-2018: Dry Statewide with a Big Chill on the way East of the Divide

Issue Date: Thursday, September 27th, 2018
Issue Time: 08:05AM MDT

— Flooding is NOT expected today

After some of the coldest morning temperatures of the season to start the day yesterday, most places warmed up considerably during the day as high pressure sliding off to the east ushered in warm southerly winds. With high pressure at the surface and very dry air throughout nearly the whole depth of the atmosphere, precipitation chances are essentially zero statewide today and temperatures are expected to be near or a bit above seasonal averages. There is, however, a strong cold front lurking to our north, and while it will be unable to break the dry pattern across Colorado, it will mean the coldest day of the season so far east of the divide come tomorrow. The front’s late-morning position today has been drawn on the map below, with moister areas on the water vapor imagery nicely highlighting the influence of the jet stream and cold front. Further south, desert air sits over much of the state with just isolated pockets of high-level cloudiness across the northern tier of the state.

As the jet stream once again dips a little further south over the northern plains, it will help to push the cold front further south today and tonight, but it should remain north of Colorado through this evening. By the early morning hours of Friday, it will have passed through most of northeastern Colorado, and should reach southern Colorado by mid-day tomorrow. The pool of cold air associated with this feature is quite shallow, so the dramatic drop in temperatures may not even be felt in the mountains and foothills above 8000-9000’ above sea level. Many locations in the northern plains and urban corridor may experience their high temperatures for tomorrow at midnight tonight, as temperatures may drop 20+ °F behind the front and only recover into the 50s °F during the day tomorrow. In short: little in the way of sensible weather across Colorado today, but big changes are on the way for the eastern half of the state overnight.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Northwest Slope, Northern Mountains, Grand Valley, Central Mountains, Southwest Slope, San Juan Mountains, San Luis Valley, Southeast Mountains:

Mostly sunny and seasonably warm today as predominantly southwesterly winds carry dry desert air into the region. Low relative humidities may enable some growth of active fires like the Silver Creek and Ryan fires, but wind gusts and temperatures should be low enough to prevent any errant behavior or rapid growth. A few clouds may drift overhead from time to time across the northern half the state. Tonight’s cold front will not affect these areas.

Front Range, Urban Corridor, Northeast Plains, Palmer Ridge, Southeast Plains, Raton Ridge:

A mostly sunny and seasonably warm day is in store for the northeast 1/3rd of the state today, with temperatures running around 5-10°F above normal. Expect the cold front to reach the northeastern corner of the state after midnight tonight and be through the Palmer Ridge by sunrise Friday. Southeastern reaches of the state will not be affected by the front until tomorrow morning.

FTB 09-26-2018: Fall Finally Takes Hold over Colorado

Issue Date: Wednesday, September 26th, 2018
Issue Time: 08:25AM MDT

— Flooding is NOT expected today

After a long stretch of hot weather to begin September over much of Colorado, a series of cold fronts over the past few days have finally begun to usher in more fall-like temperatures. In fact, many locations in the plains had their coldest temperatures of the new cold season so far today, ranging from just below freezing in spots to the low 40s °F across the southern plains. The cooler temperatures are the result of Canadian surface high pressure, which has been shunted southward into the region by northwesterly winds aloft. A compact and fast-moving shortwave trough (dashed red line) is embedded in the upper-level flow, providing just enough lift to produce a few clouds from the Front Range and Denver metro to points southeast. These features are illustrated in the annotated map of satellite water vapor imagery below.

As this shortwave zips off to the east this morning, drier air will take hold, leading to mostly clear skies across much of the state for the middle part of the day. The exception to this will be along the southern tail of this feature, which may still have enough energy and moisture with it to fire up some isolated thundershowers across the far southern tier of counties in the state. A few forecast models indicate convection starting late this morning that should push rapidly off to the southeast, possibly visiting the northern portions of the Raton Ridge and before pushing out of the state. The limited moisture and strong winds aloft will limit both the intensity and persistence of these showers and storms, and therefore no flood threat is anticipated. Additionally, more clouds may work their way into the northern reaches of the state by this evening, associated with the next push of shortwave energy.

 

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

San Juan Mountains, San Luis Valley, Southeast Mountains, Raton Ridge, and Southeast Plains:

Cloudy and seasonably cool to start with this morning. Isolated to scattered showers may build late this morning, initially across the higher terrain. These may survive the push off the mountains onto adjacent lower terrain in the San Luis Valley, Raton Ridge, and western Southeast Plains. Any rain that does develop will be pushed along by robust winds aloft, thereby limiting any flooding potential. Rainfall rates will generally be in the 0.05 to 0.25 inches per hour range, and isolated spots along the New Mexico border that receive the most frequent showers today may approach 0.5 inches of total rainfall.

Primetime: 11AM to 6PM

Northwest Slope, Southwest Slope, Grand Valley, Northern Mountains, Central Mountains, Front Range, Urban Corridor, Northeast Plains, Palmer Ridge:

Clearing skies this morning with temperatures running just a few degrees below seasonal normals. Expect a strong warm up today with plenty of sunshine and winds turning westerly over western portions of the state and southeasterly on the eastern plains. Mid- and high-level clouds may begin working their way into northern portions of the state by the evening, but no precipitation is anticipated.

FTB 09-25-2018: Scattered Storms Expected over the Southeast Mountains and Raton Ridge with Cooler Temperatures Forecast Statewide

Issue Date: Tuesday, September 25th, 2018
Issue Time: 09:05AM MDT

— Flooding is NOT expected today

A secondary cold front dropped through the state early this morning and is currently over the Texas panhandle. Breezy northerly winds are being experienced behind the front over the eastern plains this morning with temperatures in the mid 40Fs to 50Fs. A Frost Advisory has been issued for the northern Front Range and Urban Corridor tonight as temperatures today will only reach the mid-60Fs and drop to 28-32F overnight due to the cold air mass remaining in place and light winds. Increased low-level moisture behind the front has created some light upper-level clouds over the Front Range and along the front, but the shallow moisture is mixing out quickly with the sunrise. Despite the cold front passage, the northern 2/3 of Colorado already has dry air filling in behind the front. This can be noticed by the shades of yellow over the majority of the state. The exception is over southern Colorado where a little better moisture is able to hold on with more westerly flow aloft rather than northwesterly flow aloft. Upslope flow is expected to initiate showers and weak thunderstorms this afternoon with surface winds turning from more northerly to northeasterly over eastern Colorado. While some spotty, light showers may form over the high terrains, the best chance for afternoon rainfall is expected over the southern Southeast Mountains and Raton Ridge due to the better moisture over the region. Storms are expected to be high-based with dew points in the 30Fs, so that should limit totals with brief gusty winds possible. A few showers may linger eastward overnight into the Southeast Plains as there are some upper-level dynamics at play. Over western Colorado, skies will be mostly clear with some cloud cover likely over the San Juan Mountains this afternoon. Flooding is not forecast today.

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Urban Corridor, Palmer Ridge, Northeast Plains, Front Range, Southeast Mountains, Raton Ridge, Southeast Plains:

Temperatures today will be a 10-20F degrees cooler than yesterday with highs in the 60Fs for most of the lower elevations. Light winds tonight with the cold air mass over the region will drop overnight lows near freezing. A Frost Advisory has been issued for the northern Front Range and northern Urban Corridor due to temperatures dropping between 28 and 32F. Some upslope showers are expected this afternoon over the higher terrains. Showers to the north will be rather spotty in coverage with totals under 0.1 inches. Further south over the southern Southeast Mountains and Raton Ridge, shower and weak thunderstorm coverage will be the greatest. Storms are expected to be high-based, so some brief windy conditions are possible with max 1-hr rain rates up to 0.2 inches. A few storms may linger eastward overnight into the Southeast Plains, but totals will remain under 0.15 inches. Flooding is not expected today.

Primetime: 2:30PM to 9PM

Northwest Slope, Southwest Slope, San Luis Valley, Grand Valley, Central Mountains, San Juan Mountains, Northern Mountains:

Cooler temperatures are also expected over the northern half of these regions this afternoon with higher temperatures over the Grand Valley and Southwest Slope. Without much moisture, rainfall is not anticipated this afternoon. Expecting mostly clear skies with some scattered cloud cover over the San Juan Mountains. Today, there will also be a break from enhanced and critical fire weather. Hopefully crews are able to make some progress with the ongoing wildfires across the state.

 

FTB 09-24-2018: Trough Continues Eastward Migration and will Bringing Scattered Showers and Thunderstorms back into the Forecast

Issue Date: Monday, September 24th, 2018
Issue Time: 09:30AM MDT

— Flooding is NOT expected today

Unsettled weather is expected today as the trough continues to travel through the state. Overnight, a cold front moved across the area, so temperatures this morning were a few degrees cooler with some cloud cover over the eastern plains. Expecting cloud cover to decrease with some morning heating, which will allow a bit of instability to build before the main axis of the trough moves through eastern Colorado this afternoon. There are also some showers present this morning over the northern high terrains associated with the upper-level dynamics of the trough. Expecting these showers to slowly dissipate through the morning hours. Shower and thunderstorms coverage will pick up over the San Juan and Central Mountains early this afternoon where instability is able to mix with some moisture. These high-based storms are expected to be rather scattered and weak in nature with some brief, gusty winds possible. Over the Northwest Slope, drier air will fill in behind the trough. This will bring back low relative humidity values, and paired with gusty surface winds and dry fuels, bring back critical fire weather. A Red Flag Warning has been issued through this evening with winds in the 15 to 20mph range and gusts up to 35mph possible.

As the cloud cover begins to burn off behind the front, a bit of instability will be able to build over eastern high terrains and the eastern plains north of the Palmer Divide. Enhanced low-level moisture behind the front and moisture associated with the trough will allow the return for showers and thunderstorms to the forecast. Precipitable Water (PW) at Denver this morning was measured at 0.45 inches with a nice dry layer between 500 and 350mb. This should be enough moisture for some scattered showers this afternoon and evening though totals will be a bit lighter with the dry layer. Expecting storms to initiate over the Front Range by midday and move into the adjacent plains by early afternoon. Some more isolated showers are expected over the Southeast Mountains. As storms move into the adjacent plains off the Front Range, better low-level moisture will allow rain rates to increase though decent storm motion should keep totals under 1 inch. The stronger thunderstorms this afternoon will likely produce some gusty winds. The highest totals are expected to be over the northeast corner of the state along the NE/CO border. A secondary cold front will surge south through the state overnight into tomorrow morning, so expecting more cloudiness and light showers tomorrow morning with some cooler temperatures. As anticipated, flooding is not expected today.

 

Today’s Flood Threat Map

For more information on today’s flood threat, see the map below. For Zone-Specific forecasts, scroll below the map.

Zone-Specific Forecasts:

Northwest Slope, Southwest Slope, San Luis Valley, Grand Valley, Raton Ridge, Southeast Plains:

Not expecting much precipitation over these regions today. Dry air will fill in behind the trough over the northwest corner of the state, which will drop relative humidity values. With surface winds in the 15 to 20mph range, critical fire weather is expected. A Red Flag Warning is in place through this evening. Rainfall this afternoon should be confined to the southern high terrains for western Colorado, which means the Southwest Slope, Grand Valley and San Luis Valley will miss out on the action as well. The Raton Ridge and Southeast Plains are also expected to stay mostly dry with downsloping winds expected over the Southeast Mountain. A stray storm could wander into the Southeast Plains off the Palmer Ridge, but with dew points in the 30Fs cloud cover is more likely than wetting rainfall.

Urban Corridor, Palmer Ridge, Northeast Plains, Front Range, Southeast Mountains, Central Mountains, San Juan Mountains, Northern Mountains:

Some upslope showers are expected this afternoon over the higher terrains. Scattered storms over the southern and western mountains will be high-based, so max 1-hr rain rates should be limited to 0.15 inches with some gusty winds possible. Best moisture will be over the Front Range, so expecting shower coverage to be greatest over this area. Max 1-hr rain rates up to 0.3 inches are possible. Storms are expected to move into the Urban Corridor, Northeast Plains and Palmer Ridge early this afternoon. With a bit better moisture, max 1-hr rain rates up to 0.4 inches (south) and 0.75 inches (north) are possible. Expecting winds to pick up as well this afternoon with the upper-level jet mixing stronger winds down to the surface. Another cold front moves into the area early tomorrow morning, so some light showers may be possible over the Northeast Plains as the front slides south.

Primetime: 11AM to 12AM