Special Weather Statement, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
233 PM MDT Tue Apr 27 2021

.SHORT TERM...(This evening through Wednesday)
Issued at 230 PM MDT Tue Apr 27 2021

The uncertainty in the forecast remains quite high. The
convection hasn't been well handled by the convective allowing
models, as the stronger storms initially developed just east of
the I-25 Corridor. We've had a couple storms that showed brief
signs of rotation, but the surface boundary has pushed south of
the Colorado Springs area, and thus taking most of the isolated
tornado threat to the far southeast side of our forecast area
(Limon and points south/east). We've had isolated severe hail, but
the majority of these storms are producing a considerable amount
of small hail, and in some cases deep enough to be considered
"plowable". We see these same trends continue through the evening,
and storms should become more organized/widespread as they reach
even more unstable air over the northeast plains where SBCAPE is
near 1000 J/kg. There are even pockets of higher CAPE in metro
Denver where sunshine popped out for a couple hours this afternoon
so threat is still not over.

Later this evening into the overnight hours, we should see a
transition to more widespread precipitation as a deeper upslope
flow develops, and some weak frontogenesis stretches out across
northeast Colorado. Deep and rich moisture source will support
moderate to heavy precipitation amounts, with another one half to
one inch of liquid equivalent precipitation expected overnight.
Snow levels will drop to around 5500-6000 feet, with a rain snow
mix down to about 5280 (Denver). Wet bulb temperatures in the
35-37F range will make it hard to snow or even accumulate below
6000 feet, but there is potential for Advisory criteria snowfall
over the Palmer Divide. That said, the confidence of heavier
precipitation there is lower as they could be on the southern
fringe of the more significant precipitation shield overnight. We
do have higher confidence in the foothills, so we'll add the
Southern Front Range foothills to a Winter Weather Advisory. The
rest of the Front Range Mountains and Northern Foothills will stay
a low end Warning at this point.

The rain and snow will continue Wednesday morning with persistent
upslope flow and deep moisture. Precipitation rates will be
decreasing by mid to late morning with rain and snow ending from
north to south across the area by late morning/noon hour.
However, we'll see enough instability for redevelopment of
scattered showers for the afternoon.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 230 PM MDT Tue Apr 27 2021

Precipitation should be out of the area by the evening hours
Wednesday as the trough shifts off to the south and east. Thursday
will be a bit warmer with temperatures returning to near normal
values. A substantial ridge begins building off the West Coast,
but cool northerly flow will limit how warm we get during the day.
Still, highs will be in the mid to upper 60s with mostly sunny
skies.

The ridge really dominates the forecast for Friday and Saturday.
700mb temperatures rise about 6-8C from Thursday to Friday, and
subsequently our highs increase to the upper 70s/low 80s. Saturday
looks to be the warmest day of the week, with guidance suggesting
700mb temps anywhere from 10-14C. Our forecast lies pretty close
to the middle of guidance, with highs in the low 80s to perhaps
90F over our far northeast.

The ridge flattens out and the flow becomes much more zonal as
our next trough impacts the area by the end of the weekend. The
first ripple is progged to race across the region Saturday evening
though there's not much in the way of lift. Could see a few
spotty showers in the mountains but otherwise still quiet through
Sunday morning. A stronger shortwave arrives late Sunday with
widespread Chc/Likely PoPs across the forecast area. Another round
of showers and thunderstorms is on the table for Monday, but
model solutions diverge beyond that. Early indications are that
unsettled weather will continue into mid-week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 230 PM MDT Tue Apr 27 2021

Scattered showers and storms will continue in the area through
around 01Z, and then more widespread but more stratiform
precipitation is expected to develop through the evening. Lower
ceilings under 1000 feet and visibility of 2-4SM in rain and
fog/mist should persist most of the night. This may mix with snow
after 09Z but we don't expect any accumulation as temperatures
will be marginal at best to see any snowfall. These IFR/LIFR
conditions should persist through much of Wednesday morning before
clouds begin to gradually lift toward 18Z Wednesday. Scattered
light rain showers possible into Wednesday afternoon with a likely
continuation of ILS approaches at KDEN.

&&

.HYDROLOGY...
Issued at 230 PM MDT Tue Apr 27 2021

Scattered shower and storm threat with brief moderate rain will
continue across the foothills through the early evening hours,
before widespread precipitation develops and snow levels drop to
around 7000 feet by mid to late evening. That would end any burn
area (Cameron Peak and Calwood) flood threat, which is still low.
On the plains, widespread showers and embedded thunderstorms
should result in rainfall amounts around 1 inch in most areas,
with locally 2+ inches where stronger and heavier storms persist.
We don't see any hydrology issues on the plains other than some
localized ponding of water in low lying areas and minor rises on
small streams.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until noon MDT Wednesday for COZ033-034.

Winter Storm Warning from 6 PM this evening to noon MDT
Wednesday for COZ035.

Winter Weather Advisory from 9 pm this evening to noon MDT
Wednesday for COZ036.

&&

SHORT TERM...Barjenbruch
LONG TERM...Hiris
AVIATION...Barjenbruch
HYDROLOGY...Barjenbruch

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1121 AM MDT Tue Apr 27 2021

COZ030>051-281730-
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-
1121 AM MDT Tue Apr 27 2021

...A COUPLE SEVERE STORMS, LOCALLY HEAVY RAIN, AND HEAVY
MOUNTAIN/FOOTHILL SNOW POSSIBLE...

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

.DAY ONE...This Afternoon and Tonight

Showers and thunderstorms will become more widespread across the
area through the afternoon, and a few of these storms could
become severe with hail around one inch in diameter and a low
tornado threat. The greatest risk of severe storms will be from
the crest of the Palmer Divide south of Castle Rock toward the
Limon and Akron areas. Farther north, including much of the I-25
Corridor, stronger storms will produce heavy rain and a
considerable amount of small hail.

Rainfall amounts of 1 to 2 inches are expected over much of
northeast Colorado. There is a low risk of flooding in burn areas
until about 4 pm this afternoon. A few low lying areas of the
plains could see excessive ponding and minor runoff overnight.

Snow will form over the mountains and foothills where the snow level
will start out at 8000 to 8500 feet. The snow level lowers this
afternoon and tonight. By Wednesday morning the snow level will be
close to 6000 feet. The heaviest snow is expected to fall above 7500
feet with 7 to 14 inches of snow accumulation. A few inches of
snow will also be possible over the Palmer Divide.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Light precipitation will linger through the day Wednesday, with
snow above 6500 feet and rain below 6500 feet. Snow accumulations
in the high mountains could be up to 4 more inches. Dry weather
is expected Wednesday night into Sunday. The next system will
move in with a chance of precipitation for most of the forecast
area Sunday night through Monday night. It will be snow in the
mountains. Temerptures will be below seasonal normals on Wednesday,
near normal on Thursday and above normal Friday through Sunday.
Cooler temperatures are expected Monday.

.SPOTTER INFORMATION STATEMENT...

Spotter reports of hail, wind, heavy rainfall, and snow will be
appreciated.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Service Notice</title>
  <link rel="stylesheet" href="index.css">
</head>
<body>
  <main class="wrap">
    <section class="card" role="status" aria-live="polite">
      <div class="status" id="status">Temporary Notice</div>
      <h1 id="headline">This service is currently unavailable.</h1>
      <p id="message1">
        The site you requested is temporarily down for maintenance or an unexpected outage.
      </p>
      <p id="message2">
        Please try again in a few minutes.
      </p>
      <p class="small" id="detail">
        If you are an administrator, restore upstream service and remove the redirect/fallback rule when normal operations resume.
      </p>
    </section>
  </main>
  <script src="index.js"></script>
</body>
</html>

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE DENVER CO
332 PM MDT TUE APR 27 2021

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

0323 PM     HAIL             10 WSW HUGO             39.07N 103.63W
04/27/2021  M1.00 INCH       LINCOLN            CO   TRAINED SPOTTER

            LI113.

&&

Special Weather Statement
National Weather Service Denver CO
332 PM MDT Tue Apr 27 2021

COZ042-272200-
Northeast Weld County CO-
332 PM MDT Tue Apr 27 2021

...SIGNIFICANT WEATHER ADVISORY FOR NORTHEASTERN WELD COUNTY UNTIL
400 PM MDT...

At 332 PM MDT, Doppler radar was tracking a strong thunderstorm 6
miles north of New Raymer, or 30 miles north of Fort Morgan, moving
northeast at 5 mph.

Penny size hail and winds in excess of 30 mph will be possible with
this storm. Hail may accumulate on roadways causing hazardous travel.

Locations impacted include...
Stoneham and New Raymer.

A Severe Thunderstorm Watch remains in effect until 700 PM MDT for
northeastern Colorado.

LAT...LON 4061 10358 4059 10358 4053 10384 4075 10400
      4088 10372
TIME...MOT...LOC 2132Z 241DEG 6KT 4070 10380

BOWEN