Severe Thunderstorm Warning 5, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
514 PM MDT Fri May 5 2023

.SHORT TERM...(This evening through Saturday)
Issued at 145 PM MDT Fri May 5 2023

A trough is parked over the Pacific Northwest this afternoon with
a moderate to strong southwesterly flow aloft over the forecast
area. One weak embedded short wave still move across the region
through early this evening, then another clips northwest Colorado
late tonight into Saturday morning.

This afternoon, the most persistent area of weak thunderstorms has
been over the foothills of Larimer and Boulder counties and this
has shifted to the I-25 corridor north of Fort Collins. Along
the urban corridor, the main threat would be gusty outflow winds
to 50 mph and brief light rain showers. There is still a marginal
to slight risk of severe thunderstorms east of a line from around
New Raymer to northeast Weld County to Last Chance in southwest
Weld County, where the best moisture will be. SPC MLCAPE analysis
has values aoa 500 J/kg in this area, with damaging wind gusts and
hail up to one inch possible, can't rule out a brief tornado.

For tonight, the first wave of convection should shift to the
north and northeast of CO by late evening. There will be an
increase in shower activity over the mountains with the passage of
the second system late tonight, around 09z. Mid levels will be
slightly cooler on Saturday with dry southerly winds developing
across the Palmer Divide and eastern plains Saturday afternoon.
Less shower/tstm coverage overall, and most confined to areas
along our northern border. Reference the fire weather discussion
the Red Flag highlights.

.LONG TERM...(Saturday night through Friday)
Issued at 145 PM MDT Fri May 5 2023

Southwest flow aloft will continue to prevail over Colorado
through this weekend and through at least Wednesday. Mild and
mostly dry air will accompany the southwest flow into the area.
Precipitable water values will be near to slightly below normal.
Not much change in temperatures over the next few days, with highs
in the 70s across northeast Colorado. A closed low will move into
California and Nevada Tuesday. This should lead to increasing
southwest flow aloft Tuesday. At the surface, a low or low
pressure trough should form somewhere across central or eastern
Colorado. To the east of it, east to southeast winds are expected
to transport moisture into the area. Will have an area of higher
PoPs over the northeast plains for this. Otherwise for Sunday and
Monday, any convection is expected to be weak due to the limited
moisture and instability.

For Wednesday through Friday, there remains a fair amount of
uncertainty on the large scale pattern. The 12Z GFS and 00Z ECWMF
show a closed low lifting north of Colorado during this period.
On the backside of the low, a wave intensifies and digs south to
the Southern Rockies by Friday, not a common pattern. However, the
12Z Canadian, 12Z ECMWF, and some other ensemble members keep the
idea of a closed low moving across the Central and Southern
Rockies. Both scenarios would bring cooler temperatures starting
Thursday and a good chance for precipitation. Biggest question
mark is Wednesday, which is when we start to transition from a
southwest flow aloft to troughiness.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 514 PM MDT Fri May 5 2023

Lots of microbursts/boundaries to deal with this afternoon.
Fortunately, we're transitioning to a somewhat steadier flow as a
boundary has brought west/southwest winds into the TAF sites and
convection has moved slowly east. Those winds will likely turn a
bit more northwesterly through 02Z-03z as we get more influence
from cooler light shower outflows over Larimer County as of 23Z.
Eventually we become light and variable and should settle back to
light south/southwest winds around 10 knots by 07Z.

Winds on Saturday may be difficult again, but highest probability
would be to settle toward southeast winds 18Z-21Z, and then
perhaps mixing to west/northwest wind gusty winds to 20-25 knots
possible thereafter. We don't see any threat of thunderstorms
tomorrow, but some virga is possible with just a slight chance of
a variable gusty wind after 21Z.

&&

.FIRE WEATHER...
Issued at 145 PM MDT Fri May 5 2023

Critical fire conditions will be over eastern Elbert and Lincoln
counties until 7 pm due to gusty south to southwest winds and low
humidity levels. Similar conditions are expected on Saturday, so
the Fire Weather Watch has been upgraded to a Red Flag Warning.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM MDT this evening for COZ246-247.

Red Flag Warning from 11 AM to 8 PM MDT Saturday for COZ246-247.

&&

SHORT TERM...Cooper
LONG TERM...Meier
AVIATION...Barjenbruch
FIRE WEATHER...Cooper

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1053 AM MDT Fri May 5 2023

COZ030>051-061700-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
1053 AM MDT Fri May 5 2023

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

Isolated severe thunderstorms will be possible over the far
northeast plains this afternoon. Large hail, strong winds and
possibly a tornado may occur. The best focus will be north of a
Fort Morgan to Akron line.

Elsewhere there will be a chance of showers and a few thunderstorms
across the higher terrain and along the I-25 Corridor. Wind gusts
to 50 mph may accompany this activity.

Finally, critical fire conditions will be in place over eastern
Elbert and Lincoln counties today due to gusty winds and low
humidity levels.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

On Saturday and Sunday there will be weak showers and storms that
develop mainly over the higher terrain. These will not produce much
precipitation so the burn area flash flood threat is very low.
Elevated to critical fire weather conditions will develop across the
plains due to dry and windy weather. The worst fire weather
conditions will be in Elbert and Lincoln Counties on Saturday and a
Fire Weather Watch is in effect as a result.

Monday and Tuesday will be warmer with weaker winds. Coverage of
showers and storms will be very low. By the end of next week, there
is a chance of more widespread precipitation for our forecast
area which could increase the threat of flash flooding in the
recent burn areas.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight.

Special Weather Statement
National Weather Service Denver CO
429 PM MDT Fri May 5 2023

COZ048-050-051-052315-
Phillips County CO-Sedgwick County CO-Logan County CO-
429 PM MDT Fri May 5 2023

...A strong thunderstorm will impact portions of east central Logan,
northwestern Phillips and Sedgwick Counties through 515 PM MDT...

At 429 PM MDT, Doppler radar was tracking a strong thunderstorm near
Haxtun, or 19 miles west of Holyoke, moving northeast at 30 mph.

HAZARD...Wind gusts up to 50 mph and half inch hail.

SOURCE...Radar indicated.

IMPACT...Gusty winds could knock down tree limbs and blow around
         unsecured objects. Minor damage to outdoor objects is
         possible.

Locations impacted include...
Haxtun, Ovid, Sedgwick, Fairfield and Marks Butte.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

If outdoors, consider seeking shelter inside a building.

This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.

A Severe Thunderstorm Watch remains in effect until 1100 PM MDT for
northeastern Colorado.

&&

LAT...LON 4085 10212 4055 10259 4066 10282 4100 10256
      4100 10245
TIME...MOT...LOC 2229Z 220DEG 28KT 4068 10265

MAX HAIL SIZE...0.50 IN
MAX WIND GUST...50 MPH

HEAVENER

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DENVER CO
432 PM MDT FRI MAY 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0411 PM     DUST STORM       BENNETT                 39.76N 104.42W
05/05/2023                   ADAMS              CO   DEPT OF HIGHWAYS

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DENVER CO
509 PM MDT FRI MAY 5 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0504 PM     HAIL             4 N HAXTUN              40.70N 102.63W
05/05/2023  M0.88 INCH       PHILLIPS           CO   TRAINED SPOTTER

&&

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