Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 031537
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
937 AM MDT Wed Jun 3 2020

.UPDATE...
Issued at 935 AM MDT Wed Jun 3 2020

Some indications that it will take a bit longer for moisture to be
flushed out of Weld County later this morning and into the
afternoon, so may see some stronger storms with the chance of hail
a bit further west than thought. Looking at forecast soundings
around the area of the new 12Z NAM still has strong outflow winds
the most likely hazard from storms over the high terrain and urban
corridor. Some high res models including the HRRR, HRRR-X and RAP
are showing good potential for strong outflow winds moving out of
Larimer County this afternoon and into the evening, spreading
east-southeast across the plains. Best CAPE values still being
shown over the far northeastern corner of the state this afternoon
into tonight, where the Slight Risk of severe storms from SPC
remains. No big adjustments need to make to the current forecast,
as we still have good PoPs for Weld County, the storms just may be
a bit stronger.


&&

.SHORT TERM...(Today and tonight)
Issued at 300 AM MDT Wed Jun 3 2020

The upper level ridge will be centered over southern AZ/NM today.
In addition, a weak upper level disturbance will pass to the
north and east of CO this afternoon, allowing for a moderate
northwesterly flow aloft. At the surface, low level moisture
along the urban corridor and northeast plains will start to mix
out from west to east later this morning. A dryline boundary will
then set up around Sterling to Limon by this afternoon and act to
initiate isolated to scattered thunderstorms. Surface based CAPES
of 1400-1600 j/kg generated by the HIRES models around Sterling
this afternoon. Best combination of jet support aloft and
instability at the surface will this region. As a result, there
will be a slight risk of severe thunderstorms primarily for Logan,
Sedgwick, Phillips and Washington counties this afternoon and
evening. Main threats will be large hail and damaging wind gusts.

Elsewhere, a drier westerly flow at the surface and aloft will
lessen the risk of severe thunderstorms, although there may be a
brief marginal risk east of a line from Greeley to Limon. By this
evening most of the thunderstorm threat should be well east of
Denver with just some weak residual showers around. The hot
weather will continue this afternoon with temperatures back near
90 for Denver.

.LONG TERM...(Thursday through Tuesday)
Issued at 300 AM MDT Wed Jun 3 2020

Upper level ridge will slowly slide east across the Central and
Southern Rockies Thursday and Friday. By Friday evening, this
ridge will be pushed east of Colorado by an upper level trough
moving across the Desert Southwest and Great Basin. It will be
very warm Thursday and Friday with highs around 90 degrees. Friday
looks to be the warmest day with lower 90s expected to be more
common. As far as thunderstorm chances go, westerly flow aloft and
at the surface will help dry the airmass. The dry line will be
east of Colorado Thursday. There should be enough instability and
moisture to generate isolated high based showers and
thunderstorms. Main threat with this will be gusty outflow winds.
A surface high drops south over the Northern Plains Friday and
produces an easterly upslope flow over eastern Colorado. This will
increase low level moisture and increase instability. Even with
the increase in moisture and instability, warm air aloft
underneath the ridge axis may cap convection. However, if storms
are able to form, some them may become severe.

The trough moving in from the Pacific lifts north/northeast
across the Desert Southwest, Great Basin, then the Northern
Plains. Models still differ on the track and timing of this. Best
lift with this system is expected to be over the western half of
Colorado, where showers and thunderstorms are likely to accompany
the trough as it lifts across the region. There is more
uncertainty regarding shower and storm develop over eastern
Colorado. Depending on the track of this system, strong southerly
winds will be possible across eastern Colorado.

Strong southwest flow aloft will be in place Sunday and Monday as
an upper level low moves over the Pacific Northwest and Northern
Rockies. This is expected to bring dry and windy conditions both
Sunday and Monday, raising the fire danger. A short wave trough
will move into the Great Basin Monday. At the surface, a low
develops over eastern Colorado and a cold front drops south across
eastern Colorado late Monday. Depending on the timing, this could
bring showers and thunderstorms Monday evening and Monday night.
The upper level trough then tracks across Colorado on Tuesday. It
will be cooler Tuesday under the trough and behind the cold front.
Showers and thunderstorms will also be possible with this system
Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday night)
Issued at 935 AM MDT Wed Jun 3 2020

Generally VFR expected today. Westerly winds this morning will be
veering around to a northerly to northeasterly direction by this
afternoon. However some convection over the mountains may produce
more northwesterly winds due to the outflow pushing out over the
plains. May need to change the TAFs to show more of a NW component
around 21z. Drier high based convection is expected over the
urban corridor, could start as early as 19Z, with best chance to
be near APA. Main focus for stronger thunderstorms should be east
of the terminals this afternoon. A surge of northwest winds this
evening is being depicted on several high resolution models,
moving out of Larimer County. Have changed the change groups after
00z to be northwest, but may need to increase the speeds. Winds
should then shift to southeasterly later this evening then
southerly tonight.


&&

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

$$

UPDATE...Kriederman
SHORT TERM...Cooper
LONG TERM...Meier
AVIATION...Kriederman



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