National Weather Service Forecast Discussion

000
FXUS65 KBOU 252346
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
546 PM MDT Sun Sep 25 2022

.SHORT TERM...(This evening through Monday)
Issued at 158 PM MDT Sun Sep 25 2022

Just some thin high clouds over the CWA at this time. Winds are
pretty weak for most of the CWA right now.

Models have an upper ridge on top of the CWA. The weak northwesterly
flow aloft tonight becomes ever weaker and variable on Monday.
There is a weak low level pressure gradient over the CWA. The
airmass is fairly dry. There is little instability. Will go with
dry and little cloudiness. For temperatures, Monday`s highs are
1.5 to 3.0 C warmer than today`s highs.

.LONG TERM...(Monday night through Sunday)
Issued at 158 PM MDT Sun Sep 25 2022

A ridge at 500 mb will continue to dominate our weather through
midday Thursday.  The center of the 700 mb ridge is pretty much
squarely over Colorado on Tuesday, and temperatures range between
+8 and +12 degC, with the coolest temps at 700 residing across
the northeast corner of Colorado, closest to the deep trough over
the Midwest. Highs should be in the upper 70s to around 80 across
the plains, with 60s to around 70 in the mountain valleys. Winds
across the plains should remain under 20 mph other than a few
gusts, and RH should stay above 20-25 percent so no real fire wx
concerns either. There is a bit of moisture that works under the
ridge, so can`t rule our scattered showers and storms mostly
across the central mountains east to the Palmer Divide. It`s
doubtful the showers will survive east of the foothills.

More of the same for Wednesday, but 700 mb temps warm 1-2 degC vs
Tuesday, translating into highs pretty much all in the low 80s
across the plains, and 60s to around 70 deg in the mountain
valleys. It will be breeziest along the far eastern plains east
of Fort Morgan to Limon, where gusts to 25 mph are expected but RH
again should be above 25%. PW values drop to around 0.4" (0.1-0.2"
less than Tuesday) so afternoon convective coverage in the
mountains will probably just be isolated. Best chances (which are
quite low) would be over Park and Summit Counties.

A decent short wave trough moves across the U.S.-Canadian border
on Thursday with a trough axis extending south to the Great
Basin. This feature finally shoves/flattens the ridge off to the
east. However, the approaching trough axis actually advects warm
air at 700 mb out of the west, and temperatures should be very
similar to Wednesday`s across the area. Ahead of the trough axis
some sub-tropical moisture works into Colorado, once again
raising PoPs given PW should increase to 0.5-0.6" all across the
high country, especially along and west of the Divide. Because
it`s mostly west flow the best chances of precip are across the
high country east to the eastern foothills, but given straight
west flow aloft, the I-25 corridor and plains to the east will be
downsloped, and surface dewpoints in the 30s mean any storms that
move east off the mountains will not survive long. Sprinkles and
gusty winds are likely the main impact across the I-25 corridor,
and not much east of there. Winds should be well below red flag
criteria during the afternoon but it will be very dry with RH
dropping to about 15% across the plains.

Friday and beyond the forecast is much more uncertain.  Ensemble
solutions move a cold front across our area on the backside of the
short wave trough which by Friday evening should be across
Montana or North Dakota. EC ensemble solutions hold the trough
axis just west of us, cutting a part of the trough off Saturday
into Sunday, while GEFS deepens the trough over North Dakota and
it just wobbles around all weekend. Needless to say there is thus
major spread in the ensemble solutions for the weekend with the
GEFS being warmer and drier, and the EC cooler and wetter. First,
Friday looks to be pretty warm until FROPA, with highs around 80
across the plains and 60s to around 70 in the mountains. Most of
the EC ensemble members generate upslope precipitation behind the
front across much of our area east of the Divide, starting late
Friday and continuing into early Saturday. Highs Saturday are
thus much cooler, but within the EC ensemble there is large
spread. With the trough well north of us in the GEFS solution,
only about 1/3 of the GEFS members generate precipitation along
and east of the Divide. Nevertheless, with a trough "nearby" and a
frontal passage, precip chances look decent early this weekend
and the temperatures will trend downward especially on Saturday.
Snow levels this weekend should remain above 11kft elevation
because the air associated with the trough does`t look
particularly cold.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 546 PM MDT Sun Sep 25 2022

North to northeast winds will be a little slow to return to normal
drainage winds, but we should see more of an east/southeast
component toward 02Z-03Z with a return to south/southwest winds
around 10 knots by 06Z. On Monday, winds will become
light/variable 15Z-18Z, and then turn more north/northeast at
10-15 knots after 18Z. VFR conditions will persist with mostly
clear skies.

&&

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

$$

SHORT TERM...RJK
LONG TERM....Schlatter
AVIATION...Barjenbruch

NWS BOU Office Area Forecast Discussion