559
FXUS65 KBOU 191702
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1102 AM MDT Thu Sep 19 2024

.KEY MESSAGES...

- Dry and warm through Friday with elevated fire weather
  conditions.

- Storm system will impact the area this weekend. 70-80% chance
  of precipitation, but considerable uncertainty regarding how
  much. There is a chance of significant rainfall, and several
  inches of mountain snow depending on track/evolution.

- Turning much cooler by late Saturday and Sunday. Below normal
  temperatures early next week, then likely (60% chance) back to
  drier and warmer weather toward the middle of next week.

&&

.UPDATE...
Issued at 1101 AM MDT Thu Sep 19 2024

Satellite pictures indicated a few clouds over the mountains at
this time. Normal diurnal wind patterns were indicated over the
plains. Temperatures were already in the lower and mid 70s F over
the plains with mid and upper 50s in the mountains. Not to much to
change with the grids, just some minor temperature and wind
alterations this update.

&&

.SHORT TERM /Through Tonight/...
Issued at 353 AM MDT Thu Sep 19 2024

Southwest flow aloft continues today as an upper level low dives
south along the California coast. Ridging in the southwest flow
aloft will lead to weaker flow and less wind today. The airmass
remains dry with mostly sunny skies. The dry conditions will
elevate fire weather conditions this afternoon. Winds will be a
little weaker than yesterday. The mountains and higher foothills
may see southwest gusts of 25-30 mph. Temperatures will be similar
to what we saw yesterday with highs in the lower to mid 80s over
northeast Colorado.

For tonight, dry conditions continue with only some high clouds
lifting north across the area. Mild overnight lows are expected
with upper 40s to mid 50s over northeast Colorado.

&&

.LONG TERM /Friday through Wednesday/...
Issued at 353 AM MDT Thu Sep 19 2024

The last day of above normal temperatures and dry conditions ends
Friday. Cross sections display strong southwest flow and weak mid-
level moisture leading to a few high clouds along the eastern
plains. With mostly sunny skies, afternoon temperatures will reach
the mid to upper 80s along the plains. Additionally, higher
elevations are expected to reach the low 60s to mid 70s. The
combination of dry conditions and increasing low level southwest
winds could lead to near critical fire weather conditions mainly for
the Palmer Divide and adjacent plains. Winds remain borderline with
gusts up to 20-22 mph. As the incoming trough approaches
northeastern Colorado, winds shift northwest overnight into Saturday
morning.

Recent models runs have introduced a southerly track which has
delayed incoming precipitation. There is good agreement between the
ECMWF, GFS, and Canadian where the center of the upper level low
reaches the Four Corners starting late Saturday afternoon. There
were concerns on previous runs with convective development
occurring along the higher elevations before the bulk of the
system arrives to northeastern Colorado which could lead to a
greater flash flood threat for recent burn areas. This outcome
has lowered due to rain becoming more stratiform and this should
ease the flash flood threat over the burn areas. In terms of QPF,
GFS ensemble members have a greater spread from 0.2-3.50 inches
versus the ECMWF ensembles therefore there is still large
uncertainties in precipitation amounts. With significant
differences, decided to lean towards a blend NBM and ECMWF of
0.60-2.20 inches total precipitation for the plains and Palmer
Divide. Areas such as northern Weld, Logan, Sedgwick and Phillips
may receive higher totals depending on flattening ridge south of
our region. Additionally, decided to increase PoPs both late
Saturday through early Sunday to reflect higher confidence in
timing of rainfall for the plains and snow for areas above 11-12k
feet. Snowfall totals between 3-6 inches could occur and those
traveling to areas such as Berthoud Pass should prepare for slick
roads through late Sunday morning.

Next week, models aren`t in agreement with the next trough entering
northeastern Colorado. Thus decided to lean on NBM PoPs of isolated
chances of showers across the region both Monday and Tuesday
afternoon. Temperatures remain below normal during this period.

&&

.AVIATION /18Z TAFS through 18Z Friday/...
Issued at 1058 AM MDT Thu Sep 19 2024

Models keep the east and southeasterly winds going at DIA through
the afternoon hours. Speeds should stay below 15 knots.  Drainage
winds should kick in around 04Z this evening. There will be no
ceiling issues.

&&

.FIRE WEATHER /Friday through Wednesday/...
Issued at 353 AM MDT Thu Sep 19 2024

Near critical fire weather conditions are possible along the
Palmer Divide and Lincoln county Friday afternoon. Relative
humidities drop to the lower teens. Southwesterly winds could
produce wind gusts up to 20 mph with occasional gusts up to 25
mph.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

UPDATE..........RJK
SHORT TERM......Meier
LONG TERM.......AD
AVIATION........RJK
FIRE WEATHER....AD