Area forecast discussion
National Weather Service Grand Junction Colorado
917 PM MDT Thursday may 23 2013
Update...
issued at 915 PM MDT Thursday may 23 2013
Winds gradually coming down across northwest Colorado and
southeast Utah this evening so have allowed the Wind Advisory to
expire. However...still expect locally breezy conditions to
persist through the night as we mix out at times with a fairly weak
surface inversion in place overnight. Also made some adjustment to the
red flag warnings allowing zones 290 and 292 to expire...details
on the fire weather adjustments can be found below.
&&
Short term...(this evening through Friday night)
issued at 345 PM MDT Thursday may 23 2013
Amplified trough-ridge-trof pattern continues to dominate the northern
2/3 of noam with weaker westerly flow across the southern states
and Mexico. Moisture for precipitation is pushed up against the
Front Range in the return flow around strong high pressure over
the upper Midwest...with very dry air across western Colorado back
to the Pacific. The gradient between short wave ridging over the
central rockies and the large Pacific northwest system increased
winds aloft overnight. Strong heating...and mainly clear skies are
helping bring these stronger winds aloft to the surface. Many
areas are seeing gusts over 30 miles per hour with 40 to 50 miles per hour gusts over
portions of far western Colorado and eastern Utah.
A subtle wave is seen moving through eastern New Mexico late this
afternoon and will mainly interact with moisture east of The
Divide...though a stray shower may be possible just west of this
terrain boundary through sunset. Expect a drop off of the winds
with sunset and the dry air will help develop shallow low level
inversions. There will be some winds remaining in the high country
overnight with Lee down-sloping winds and windward ridge-top
winds keeping things mixed at times. As a result locally critical
fire weather concerns will remain in areas of the southern County Warning Area
where fuels remain dry and relative humidity recovery will be minimal. Surface low
pressure be lifting north overnight as the jet rounds the trough to
the west. This slackens the gradient across the western slope and
weakening down valley winds...with slightly cooler minimums will
result.
As the upper low to the northwest absorbs the jet and vorticity lobe it
will be re-orienting east to west...with a reduction in the middle
level gradient aloft. This should negate the chances of advisory
level winds but strong heating and afternoon mixing will be enough
to keep a threat of critical fire weather conditions in place
across southwest Colorado as winds gusts over 25 miles per hour. 700 mb temperatures
will take a slight dip tomorrow and highs may be a one or two
degrees cooler in places but still running well above normal under
mainly clear skies. Again expect winds to quickly take a down turn
near around sunset tomorrow evening with lows dropping off to near
or slightly above normal in this warm regime.
Long term...(saturday through thursday)
issued at 345 PM MDT Thursday may 23 2013
The elongated trough remains near the West Coast through the
weekend. Dry...warm conditions combine with gusty SW winds into
Memorial Day. Daytime temperatures expected to stay 7-10 degrees
above normal through the weekend. Temperatures are forecast to lower
to near normal by Memorial Day but this seems overly fast.
The models are in better agreement for the trough progression early
next week...though the favored ec is still slower. Chances of
showers start as early as Tuesday as the negatively tilted is
oriented from Oregon into southern Arizona. Precipitable water
values increase to near 0.6 inches. The trough approaches the region
on Wednesday for increasing moisture and cooler temperatures with a
weak cold frontal passage timed for Wednesday or Thursday. Accepted
slight chance probability of precipitation through these periods in this forecast package
but will raise them significantly tomorrow if model timing is
consistent.
&&
Aviation...(for the 06z tafs through 06z Friday night)
issued at 915 PM MDT Thursday may 23 2013
Dry southwest flow will remain in place through Friday night with
VFR conditions persisting at all sites. Gusty winds will
continue...especially near ridge tops tonight and will mix back
into the valleys by midday Friday. Expect gusts to exceed 40 miles per hour
at times with areas of mechanical turbulence.
&&
Fire weather...
issued at 915 PM MDT Thursday may 23 2013
Update...red flag warnings for zones 290 and 292 have been
cancelled as winds continue to come down and latest fuel status
indicates conditions have move out of critical levels as green up
continues.
Previous discussion...strong SW gradient winds were realized today
and will continue tonight. Surface based inversions will be weak
and will break at times especially in the middle-slope thermal belt
and along the north-facing slopes. Therefore the red flag warnings
for Colorado fire zones 291 and 207 have been extended through the
night and Friday. Critical fire weather conditions are possible
again on Saturday so a Fire Weather Watch was issued for zones 291
and 207. By Sunday the critical wind threshold of 25 miles per hour may not
be met so forecast certainty diminishes somewhat. Overall though
above normal temperatures...below normal relative humidity...and gusty SW winds
continue into Memorial Day.
Next week the West Coast trough of low pressure begins to push
across the inter-mountain west. This will bring a cooling trend and
a chance of showers on Tuesday through Thursday.
&&
Gjt watches/warnings/advisories...
Colorado...red flag warning until 9 PM MDT Friday for coz207-291.
Fire Weather Watch from Saturday afternoon through Saturday
evening for coz207-291.
Utah...none.
&&
$$
Update...jdc
short term...15
long term...Joe
aviation...jdc
fire weather...Joe/jdc
