Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 210249

Area Forecast Discussion
National Weather Service Denver/Boulder CO
849 PM MDT Tue Jun 20 2017

Issued at 849 PM MDT Tue Jun 20 2017

Isolated evening thunderstorms continue to spread off the higher
terrain and onto the adjacent plains. Main threats will remain
lightning from storms producing little rain, and gusty outflow
winds to 40+ mph. Enough activity upstream toward Kremmling to
keep isolated storms in the forecast til about midnight, then
should see stabilization. Warm night in store, and another hot day
tomorrow with more isolated PM storms.

UPDATE Issued at 545 PM MDT Tue Jun 20 2017

Isolated thunderstorms have already spread out as far as Fort
Collins early this evening. With continued increase in mid level
moisture from the west this evening, can`t rule out isolated
storms moving east onto the plains in the well mixed and uncapped
environment. Storms are very high based with LCLs near 18 thousand
MSL, so only brief sprinkle light rain. Main danger would be lone
lightning strikes from storm producing little if any rain, as well
as gusty outflow winds to 40+ mph.


.SHORT TERM...(This evening through Wednesday)
Issued at 251 PM MDT Tue Jun 20 2017

A strong high aloft will remain parked over the Desert Southwest
through Wednesday. This will keep a very warm west-northwest flow
aloft over Colorado. Expect high temperatures Wednesday to be
similar to today, mid to upper 90s. Record high for Wednesday is
99, a little harder to reach than the 97 today. Not much change in
moisture and instability either, with precipitable water values
around three-quarters of an inch over the lower elevations and
less over the higher terrain. Expect isolated showers and storms
to form again Wednesday afternoon. The storm bases will be high,
so chances at measurable precipitation will be low, especially
across the lower elevations. Gusty winds to 40 mph will be the
main threat with the showers and storms.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 251 PM MDT Tue Jun 20 2017

A few lingering thunderstorms may be moving slowly off the higher
terrain Wednesday night, with gusty winds and light rain. Minimum
temperatures will be very similar to tonight`s.

The upper ridge will be suppressed slightly to the southwest
beginning Thursday as several shortwave troughs drop out of
Canada around a low over Hudson Bay to bring cooler temperatures
area wide through the weekend. This will decrease most fire
weather concerns as well.  A cold front will drop into the
Colorado plains Thursday to bring slightly cooler temperatures,
though areas closer to the foothills and higher terrain may not
see the relief fast enough and readings may be similar to
Wednesday. Have warmed forecasted high readings a few degrees near
these locations to account for this. As the front pushes farther
in, upslope flow will bring a slight chance of thunder to most of
the plains through the afternoon, however the higher dewpoints
over the northeastern plains will allow for higher CAPE values,
near 2000 J/kg. With some upward QG motion progged across the area
during the same time, some severe strength storms will be
possible late afternoon into the evening. Convection will likely
continue to push the front further south, with increasing chances
of storms across the plains overnight. Models showing cooler air
along the surface may bring in stratus overnight and into Friday

Another cold push will result in highs about 15 degrees cooler on
Friday. The airmass may remain too stable and capped for any
precipitation activity over the plains, where some isolated storms
will be possible over the high terrain. GFS and NAM show more
chance for stratus with a stronger shortwave aloft and therefore
cooler temperatures compared to the EC, have trended toward the
cooler solutions.

EC then shows a stronger shortwave for Saturday, wanting to have a
high of only 63 for Denver, while the GFS is much warmer with a
high of 75. With both models showing slightly warmer readings over
the last two runs, will hedge slightly toward the warmer solution,
forecast of 70 for Denver. With high surface pressure over the
Great Plains keeping upslope flow into the area, the weekend will
feature a better chance for storms over the higher terrain above
any sort of more stable layer over the plains, and a slight chance
of showers over the plains.

The upper ridge will begin pushing back east Monday with warming
temperatures through Tuesday. A chance for thunderstorms should
return to the plains for the beginning of the week as well.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 849 PM MDT Tue Jun 20 2017

Isolated thunderstorms continue to push off the foothills and
threat will remain for the Front Range TAF sites til about 06Z
before they dissipate. Lightning and gusty outflow winds to around
35 knots expected near any showers/storms. Otherwise, VFR
conditions and light/fairly normal diurnal wind patterns will
prevail. For Wednesday, isolated showers and storms will again
form over the higher terrain and move east with gusty outflows
possible for the Denver area again after 21Z.




LONG TERM...Kriederman
AVIATION...Barjenbruch is the U.S. government's official web portal to all federal, state and local government web resources and services.