FXUS65 KBOU 230215

Area Forecast Discussion
National Weather Service Denver/Boulder CO
815 PM MDT Tue Aug 22 2017

Issued at 809 PM MDT Tue Aug 22 2017

Still some lingering isolated showers and thunderstorms over the
mountains, with much of the activity focused over Park and western
Boulder counties. Some of this will slide into Gilpin, Clear Creek
and Jefferson counties through 10 pm.  Expect much of this
activity to be finished by midnight and will just need to make
some minor adjustments to the evening forecast. The plains have
remained capped with dry conditions this evening.


.SHORT TERM...(This evening through Wednesday)
Issued at 330 PM MDT Tue Aug 22 2017

GOES-16 and current radar trends continue to show a stable
atmosphere across the eastern Plains.  As expected, convection is
primarily confined to the East slopes of the mountains. Storms
have been having a difficult time getting out of the foothills so
far. Thus, despite the 50s dewpoints hanging on along the I-25
corridor, cooler temperatures and poor lapse rates aloft have led
to stable conditions and we do not expect any convection to
survive very far east of the foothills. A Denver Cyclone has set
up near DIA with an attendant convergence zone across the eastern
side of metro Denver. A bubbling Cu field is in the vicinity of
the convergence zone and we will watch the feature the remainder
of this afternoon and evening for development given potential
instability should remain limited. Isolated storms should continue
through this evening across the mountains and foothills along and
east of the Continental Divide, diminishing with the loss of
daytime heating. Skies should become mostly clear overnight area-
wide with seasonal low temperatures.

On Wednesday the West Coast trough axis is located along the
California Coast with an upper-level ridge axis right across
Colorado. Weak westerly flow should exist in the mid and upper
levels. Models are hinting at some mid-level moisture being
advected north Wednesday afternoon and increasing PWATs a little,
up to 0.85" west of a Ft. Morgan to Limon line, and about a half
inch in the mountains. In the low levels, shallow moisture
remains in place tomorrow morning but the high res models want to
mix it out by Thursday afternoon, particularly west of Ft. Morgan
to Limon line. Eastern Colorado will have the deepest low-level
moisture and by far the best PWATs, up to 1.25" or better. Despite
the good moisture, not seeing a well defined forcing mechanism to
initiate convection across the eastern quarter of Colorado during
the daylight hours. Expect thunderstorms to form over the
mountains early afternoon and attempt to move east. If the low-
level moisture mixes out as anticipated, rain chances will be low
again along and east of the I-25 corridor. With the moisture mixed
out, temperatures will rebound across the Plains to the upper 80s
to near 90. Another decent chance of afternoon/evening
thunderstorms for the mountains and foothills, similar to the
previous few days. Mountain temperatures will be similar to
Tuesday`s with the ridge in place and lack of significant moisture
in the mid- levels.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 330 PM MDT Tue Aug 22 2017

Mid and high level moisture will increase through
Thursday. At low levels, there will be some moisture over the
eastern parts of the plains, with less near the mountains. This
means we will be marginal for surface based convection over the
plains, but likely to have storms developing over the mountains.
In addition, there is some weak synoptic scale lift moving over
on Thursday that should cause increased convection in the moist
neutral airmass. Drier air moves in on Friday, and then the
upstream ridge builds bringing the flow aloft more northerly. This
will also promote drying. There is little temperature change either
at the surface or aloft through the weekend as the northerly flow
will generally offset the subsidence.

Our forecast shows modestly higher rain chances Wednesday night
through Thursday night, then lower chances after that, mainly
over the mountains. Only minor temperature variations, probably
a few degrees cooler on Thursday due to cloud cover, then warmer
over the weekend with less cloud, and possibly a little cooler
again on Monday or Tuesday as a weak cold front drops across
the plains.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 809 PM MDT Tue Aug 22 2017

Modest southerly flow this evening at APA,KDEN and will continue
for the rest of tonight. Partial clearing of the high level deck
of clouds by later tonight. Slightly better chance for storms on
Wednesday but low areal coverage so will not mention TS in
terminal forecasts.




SHORT TERM...Schlatter
LONG TERM...Gimmestad

NWS BOU Office Area Forecast Discussion