FTB 09-30-2019: High Fire Danger Continues with Cooler Temperatures Expected by Morning

Issue Date: Monday, September 30th, 2019
Issue Time: 9:20AM MDT

— Flooding is NOT expected today

NOTE: This is the last scheduled Flood Threat Bulletin of the 2019 season. It has been a pleasure to serve you! The next Flood Threat Bulletin season begins on May 1, 2020.

Same pattern is in place over the US with a tight surface gradient creating strong, dry southwest flow over the majority of the state again today. Thinking this gradient will slightly weaken throughout the day, but fast winds and low relative humidity will create Red Flag Warning conditions again for the majority of the state. Conditions will be favorable for the rapid ignition, growth and spread of fires, so open burning is strongly discouraged. PW at Denver was measured at 0.40 inches with very dry air above 600 mb. Grand Junction’s sounding was similar, but slightly higher due to some mid-level moisture. This moisture paired with the jet overhead is helping produce some cloud cover and light rainfall over the northwest corner this morning. As the jet streak moves out later this morning and dry air above and below this mid-level layer mixes out the remaining moisture, showers should begin to diminish. Not expecting rainfall this afternoon with the dry air mass in place over the state.

At the surface, a low develops this afternoon over eastern Colorado, which may help pull in slightly higher moisture over the far southeast corner by making winds a little more southerly. If this moisture (marked by the green arrow below) can push slightly northward, overnight rainfall will be possible for Baca/southern Prowers Counties. Guidance is showing the heaviest rainfall to the south and east, but if higher PW values continues to move north tomorrow morning, some heavier rainfall will be possible on Tuesday morning. Overnight, a strong cold front starts to drop through the state, which looks to return some low-level moisture to the northeast quadrant of the state. Therefore, behind the front, some light showers and cloud cover are possible with fog to start Tuesday morning. The cooler, more fall-like temperatures will be a great way to round out the end of the heavy rainfall forecast season. As anticipated, 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:

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

Red Flag Warning is in place for the following regions minus the northern portions of the Urban Corridor, Front Range and Northeast Plains where moisture is little higher. Still expecting Elevated Fire conditions over those regions. Southwest winds in the 15 to 25 mph range with gusts up to 40 mph are expected from noon to 7PM with relative humidity values in the teens. Rainfall is not forecast this afternoon with the dry air mass overhead, and temperatures should warm quite a bit when compared to yesterday. Overnight and early morning light rain may be possible behind the passage of a strong front over the northeast quadrant of the state. Max 1-hour rain rates will remain below 0.10 inches with the best chance for accumulation over the northeast corner or northern Front Range.

Additional rainfall may be possible over Baca and southern Prowers Counties tonight if the moisture boundary shifts far enough north. If this occurs, totals up to 0.90 inches will be possible by morning (7AM), so flooding is not forecast at this time. Assuming this moisture continues to push northward tomorrow morning, some heavier rainfall may be possible from Tuesday morning (7AM) into the early afternoon (1PM). Since the FTB season is over and this is a lower end threat at best, not thinking there will be a special bulletin FTB issued at this time.

Primetime: 10PM to 7AM

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

High fire danger continues for these regions as well, although the slight increase in moisture over the Northwest Slope (from movement in the west coast low) should keep relative humidity values high enough that no Red Flag Warning will need to be issued for that region today. Ongoing showers from early this morning may produce isolated totals up to 0.30 inches. A Red Flag Warning has been issued for the Grand Valley, northern Southwest Slope and Central Mountains where southwest surface winds in the 15 to 25 mph range and gusts up to 35 mph can be expected from noon to 9PM this evening in a low relative humidity environment. High temperatures will be a couple degrees warmer than yesterday, minus the Northwest Slope and Northern Mountains due to the increase in cloud cover.

Primetime: Ongoing to 11AM