FXUS65 KBOU 290221

Area Forecast Discussion
National Weather Service Denver/Boulder CO
821 PM MDT Thu May 28 2020

Issued at 821 PM MDT Thu May 28 2020

Convection had a hard time firing off late this afternoon and
evening because of the morning cool surge and warm air aloft. 00Z
Denver sounding shows a strong cap in place near 690 mb. A few
stronger storms were able to pop through in Park County/crest of
the Palmer Divide with the higher terrain effectively minimizing
the cap there. Farther north, a couple other showers and storms
were still trying to drift off the higher terrain of the Front
Range. We don't think they'll have much luck maintaining
themselves due to the cap, but we'll keep some low pops in for the
rest of the evening based on latest radar/cloud trends. Forecast
is on track.


.SHORT TERM...(This evening through Friday)
Issued at 223 PM MDT Thu May 28 2020

An upper level ridge over the Desert Southwest today will slowly
shift east over the next 24 hours and be centered over the Four
Corners Friday afternoon. This will result in warmer temperatures
across the area Friday with highs reaching the mid to upper 80s
over northeast Colorado. With the ridge building over the region,
warming aloft is occurring. This along with cooler surface
temperatures behind this morning's cold front is helping to
stabilize the airmass. AMDAR Sounds show two caps to break. Best
chance for thunderstorms this afternoon and evening will be over
the higher terrain to the southwest of Denver. Across the Urban
Corridor and eastern plains, just a slight chance thunderstorms
survive moving off the higher terrain. The chance for storms ends
by midnight as the airmass stabilizes. Expect more instability on
Friday with MLCAPE around 500 J/kg. Scattered showers and storms
are expected to form over the mountains and foothills early to mid
afternoon and then spread eastward. The strongest storms will be
capable of brief heavy rain, small hail, and wind gusts to 50 mph.

.LONG TERM...(Friday night through Thursday)
Issued at 223 PM MDT Thu May 28 2020

For Friday night into Saturday, there is a strong upper ridge in
place over the four-corners region with a closed low sitting just
off the CA coastline. This system will push inland and north into
the Pacific northwest through Saturday with the upper jet staying
north of the region. A 700 mb low will help to pull in increased
moisture over the region with drier air in place to the west. PW
values will increase to above 0.90 inches across most of the eastern
plains Saturday with some models putting above an inch possible by
late Saturday. Diurnal storms from Friday will come to an end during
the evening hours with increasing CAA overnight with slightly cooler
temperatures for Saturday. Convection will be stunted for most of
the day given the slightly cooler and more stable conditions on the
plains, especially with most of the lift further to the north. The
lift of the day will most likely come from orographics with the
mountains seeing some convection by the afternoon hours. Flow from
the west will help to carry the storms off the mountains and over
the plains during the evening hours where steering flow remains
rather weak. This combined with the higher PW values mentioned
earlier could lead to periods of heavy rain and minor flooding under
the stronger storms. At this time models indicate elevated QPF
values for the higher terrain areas especially Park county and
eastward. Overall, look for a cooler and cloudier day with a chance
of moderate to heavy rain into the evening hours.

The northern Rockies will see another shortwave push on Sunday with
a similar picture for Colorado with modest moisture creeping in
under the upper level ridge. As the shortwave progresses eastward
the drier air to the west will start to push into western
Colorado by Sunday afternoon. There is enough CAPE and moisture
around for diurnal storms by the afternoon hours east of the
divide but with shear being on the weaker side storms will not be
as strong with the main threats being gusty winds and lightning
with heavy rain possible.

For late Sunday and into the following week there is a large trough
off the Pacific coast with a ridge stretching across the central and
southern Rockies. Colorado will be on the edge of the drier air to
the west ahead of the trough. Monday will see a chance of diurnal
convection over the higher terrain with conditions at lower
elevations staying mostly dry. Overall, the long term is looking
warmer with increasing chances of convection by mid-week with
moisture from the Gulf as well as the trough as it moves onshore
over CA.


.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 821 PM MDT Thu May 28 2020

Isolated showers and storms are mainly south of the Denver area
TAF sites, but still just a slight chance of a passing
shower/storm til about 06Z. VFR conditions will prevail, but ILS
landing conditions possible this evening due to lowering of the
ceiling to around 5000-6000 feet.

On Friday, scattered thunderstorms are expected to form over the
higher terrain after 20Z and then spread eastward through the
afternoon. Brief rain, gusty winds to 30 knots, and lightning
expected from any storms, but coverage looks limited by warm air
aloft. Main threat for the airports would be between 22Z and 03Z.




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