Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS65 KBOU 120945

Area Forecast Discussion
National Weather Service Denver/Boulder CO
345 AM MDT Mon Mar 12 2018

.SHORT TERM...(Today and tonight)
Issued at 345 AM MDT Mon Mar 12 2018

A short wave trough will move across Wyoming today and into the
Central Plains tonight. This system will increase cloud cover
across the area. Moisture and lift are limited with this system.
Cross sections show a shallow layer of moisture around 600 mb.
With added orographic lift over the mountains, some light snow
will be possible. Any accumulation will be light and should be
less than an inch.

Surface high pressure behind this system over the Northern Plains
will keep surface winds northerly today and tonight. This and
cloud cover will limit the warming. Highs should be near normal
with readings in the lower to mid 50s across northeast Colorado.
Clouds will decrease late tonight allowing for good radiational
cooling. Lows are expected to fall into the 20s for most of
northeast Colorado.

.LONG TERM...(Tuesday through Sunday)
Issued at 345 AM MDT Mon Mar 12 2018

For the big picture, large mid/upper-level longwave trough continues
to dip southward along the Pacific West Coast on Tuesday as a sharp
upper ridge migrates eastward over the Great Basin/Desert Southwest.
A powerful Pacific Jet, its core speed around 160 kts, passing south
of the West Coast trough appears to amplify the downstream ridge
moving over the Rocky Mtn region on Wednesday. Strong warming aloft
and stabilization with the passing ridge should result in ample
sunshine and unseasonably warm temperatures across the forecast
area. Model guidance is still indicating high temps in the mid 60s
to lower 70s at lower elevations and upper 40s and 50s in the high
country. See no reason to argue with that. For the record, average
high for Denver on March 14th is 54. Light flow aloft and a flat
pressure gradient should also keep wind speeds on the light side
thereby keeping the risk of large wildfires and rapid fire spread on
the low to moderate side.

Operational models and their ensemble members show the big West
Coast turning inland across the Intermountain West on the Thursday
while the upper ridge over Colorado slips east of the state. A weak
shortwave rounding the bottom of the western trough is progged to
swing newrd over the 4-corners area and eventually up over western
Colorado by Thursday evening. This may sufficiently destabilize and
saturate the column over the nrn mtns and high plains adjacent to
the nrn Front Range late on Thursday to generate a few short-lived t-
storms. However with precipitable water values on the lean side,
precip amounts should be on the light side. May actually see more
gusty outflow winds than measurable precip, particularly east of the
mtns with a dry sub-cloud environment. The increase in cloud cover
expected Thursday should knock max temps down a few degs from the
day before, and possibly down as as much as 4-6 degs according to
the ECMWF. GFS shows this wave lifting out Thursday night followed
close on its heels by a shortwave ridge which would lessen shower
chances. On the other hand, the ECMWF shows a second lobe of
moisture and energy rotating across the state Thursday night which
would rather keep showers going through early Friday morning, the
last of the which across the northeast corner of the state. Snowfall
with this system should remain confined to the higher elevations.

Friday though Saturday, the picture becomes more uncertain. Although
the GFS and EC indicate drier conditions on Friday beneath a
shortwave ridge and temperatures a few degrees above average for the
date. Uncertainty in the forecast jumps up over the weekend with
another deep upper trough digging down the West Coast. The GFS shows
this trough making a sharp turn inland over the Desert Southwest on
Saturday where it closes off and taps into a deep fetch of
subtropical moisture. Broad circulation around this nearly
stationary stacked low appears to drive waves of moisture up into
Colorado by Sunday, potentially increasing the chance of showers and
perhaps t-storms around here. Whereas, the ECMWF shows this trough
weakening and moving inland over the Great Basin, with the bulk of
its moisture and energy passing just north of Colorado on Sunday.
These two solutions would warrant the issuance two different
forecasts. Can`t do that. So will go with a blend of the two
solutions and trend slightly cooler and wetter for Sunday.


.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 345 AM MDT Mon Mar 12 2018

VFR conditions will prevail through tonight. Mid and high clouds
will increase later today with a weak system dropping southeast
across the region. Ceilings are expected to remain above 6000
feet. Southerly winds will turn to the north after 12Z and remain
a northerly component through tonight. Wind speeds should remain
light and less than 10-15 knots.




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