Area Forecast Discussion
Issued by NWS Pueblo, CO

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FXUS65 KPUB 221742
AFDPUB

Area Forecast Discussion
National Weather Service Pueblo CO
1142 AM MDT Tue May 22 2018

.UPDATE...
Issued at 1056 AM MDT Tue May 22 2018

12z model runs suggest critical fire weather conditions will be
met over a large enough portion of the San Luis Valley on
Wednesday, therefore a Fire Weather Watch has been hoisted. Low
relative humidity values combined with gusty winds will lead to
conditions favorable for rapid rates of fire growth and spread
Wednesday afternoon and evening. Although portions of the San Luis
valley have received rainfall over the past 24 hours, this has
been spotty and most areas did not receive sufficient amounts to
offset the critical fuel status. -KT

&&

.SHORT TERM...(Today and tonight)
Issued at 355 AM MDT Tue May 22 2018

...Isolated Afternoon and Evening Thunderstorms...

Twelve hundreths of an inch of rain fell at the Alamosa Airport
yesterday and now there is thick ground fog at the airport. Have
added patchy fog to the forecast for the San Luis Valley to reflect
this.  It should dissipate as the sun comes up.

A large upper low pressure area is spinning over Las Vegas, NV this
morning.  Another upper disturbance will eject northeast from the
low and cross southern Colorado today.  However, the disturbance
looks fairly weak and should generally only produce isolated
thunderstorms over the mountains and south of Highway 50.  Cannot
rule out a thunderstorm elsewhere but the greater odds are in these
areas.  Primary storm threats from most storms today will be
lightning and wind gusts to around 50 mph.  However, it looks like
storms south of Highway 50, particularly across Las Animas and Baca
Counties, could be a little stronger, producing some small hail and
locally heavy rain as well.

Otherwise, a warm and dry day is ahead for a lot of the area with
afternoon highs 5-10 degrees above average over the plains and at
least a few degrees above average elsewhere.

.LONG TERM...(Wednesday through Monday)
Issued at 355 AM MDT Tue May 22 2018

Wednesday...The upper low that had been present over the Great Basin
continues to lift northeast north of Colorado during the day. Flow
aloft over and upstream of Colorado becomes more southwesterly,
drawing up drier southwest US air over the state. Deep vertical
mixing during the afternoon will draw this dry air to the surface
across portions of the forecast area. Winds will also become breezy
across the plains and high valleys during the afternoon due to the
vertical mixing and deepening lee surface trough. Given these
conditions, there is the potential for critical fire weather
conditions to develop, primarily across the San Luis Valley.
However, winds will be borderline highlight criteria, and duration
is a concern, so holding off on highlights at the moment. East of
the dry air across the far eastern and southern plains, trailing mid-
level energy will help spur the development of isolated to scattered
thunderstorms during the afternoon and evening. Uncapped SBCAPE is
forecast to be in the 1500-2000 j/kg range over low/mid 50s dew
points. However, with the strongest flow aloft residing further to
the west, EBSHEAR values will generally be around or less than 25
knots. Given these factors, thunderstorms should stay strong to low-
end severe, with hail up to around an inch and gusty downdraft winds
the main threats. SPC agrees, highlighting the far eastern plains in
a Marginal Risk for Severe in the latest Day 2 Convective Outlook.
More isolated, weaker thunderstorms will be possible across the
mountains and adjacent plains. Temperatures will be slightly
warmer than the previous day, with highs in the mid to upper 80s
across the plains, around 80 in Colorado Springs, and the mid 70s
across the high valleys.

Thursday through Saturday...Models are in excellent agreement on
building a ridge over the eastern Rockies as a closed upper low
approaches the region from the west. The low will make landfall over
the central California coast by Friday evening, and enter the Great
basin on Saturday. The building ridge over the region and generally
southwest to sometimes westerly flow will maintain the funnel of dry
air over Colorado. Daily heating will mix the dry air to the
surface, and most likely keep the dry line east of the CO/KS border.
The lack of moisture and lack of any significant forcing under the
ridge will lead to only very isolated precip chances over the
eastern mountains each day, and far eastern plains in the event the
dry line does not mix too far east. Otherwise, expect dry and very
warm conditions during this period. Highs across the plains will
rise into the low to mid 90s, with mid to upper 80s expected in
Colorado Springs and low to mid 80s in the high valleys.  Winds
should stay light enough across the forecast area to prevent
critical fire weather conditions from developing.

Sunday through Monday...The GFS and ECMWF are in good agreement on
maintaining the upper low over the great Basin through the start of
the work week, with only minor positional differences. This will
maintain southwest flow and the fetch of dry air into southern
Colorado. Daily lee troughing and vertical mixing will lead to dry
and breezy surface conditions and potential high fire danger across
much of the forecast area. A key factor will be the status of fuels
by this time. Precip chances will likely be minimal across the
forecast area given a lack of moisture and upper forcing. Best
potential for an isolated thunderstorm looks to be over the eastern
mountains, and along the dry line near the CO/KS border if it
doesn`t push too far to the east. Temperatures will remain very
warm, with highs likely into the 90s across the plains, and 80s in
Colorado Springs and the high valleys.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1112 AM MDT Tue May 22 2018

VFR conditions expected over most of the district over the next 24
hours. The exception will be the southwest mountains where
persistent cloud cover and moisture will keep IFR conditions along
the southwest facing slopes. As thunderstorms develop this
afternoon this area will see periodic IFR conditions in
-TSRA/-SHRA. For the terminals however, VFR conditions can be
 expected with VCTS possible for both KPUB and KALS. Main threats
 will be gusty winds and lightning along with brief VFR Cigs/vis.
 Will carry a tempo group for KPUB for erratic outflow winds from
 thunderstorms this afternoon. Drier air working into KCOS should
 keep thunderstorms more distant from the terminal though outflow
 winds could still affect the TAF. Will have to watch latest radar
 trends and amend as necessary. Winds will diminish and skies
 clear tonight. Could see another round of IFR/LIFR fog at KALS
 tonight especially if area receives more spotty rainfall.

 -KT

&&

.PUB WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Wednesday afternoon through Wednesday
evening for COZ224.

&&

$$

UPDATE...KT
SHORT TERM...LW
LONG TERM...LINE
AVIATION...KT



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