Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 250900

Area Forecast Discussion
National Weather Service Grand Junction CO
300 AM MDT Fri May 25 2018

.SHORT TERM...(Today through Saturday)
Issued at 300 AM MDT Fri May 25 2018

Another very warm to hot day expected across the region today and
again on Saturday as the region comes under the influence of
increasing southwest flow aloft thanks to an approaching low
pressure system. Yesterday`s high temperatures stayed closer to
the warmer MET guidance so this forecast follows suit. Near record
highs are expected both today and Saturday due to deep mixing and
H7 temps warming to the 13C to 15C range. This means upper 80s to
low 90s today for many lower central and southern valleys and even
warmer temperatures on Saturday. Decided to go a few degrees above
guidance on Saturday as deeper mixing is expected to occur in the
prefrontal environment with very dry conditions. Also removed all
mention of precipitation for both today and Saturday as the
atmosphere remains too dry to promote any rainfall as precipitable
water values drop to below 0.3 inches across the north and below
0.2 inches across the south. These values are even lower on
Saturday. Also, not expecting much in the way of cloud cover
either. Record high temperatures look to be met or even exceeded
in some areas across the western slope today and Saturday due to
this deeper mixing and abnormally warm southwest flow. Afternoon
highs both days will be some 10 to 15 degrees above normal. To
put this into perspective, these forecast highs are closer to
late June/early July normals!

The ridge of high pressure shifts further east Saturday as the
upper level low pressure system moves into the Great Basin. A 100
kt upper level jet sets up by Saturday morning and afternoon
across eastern Utah with lapse rates increasing to an impressive 9
to 10 degrees C/km across the entire region. This means that very
deep mixing will occur up to 500 mb or higher given the lack of
cloud cover. So, when looking at H5 winds, they will peak at 50
kts across far western Colorado and eastern Utah with peak speeds
in the 30 to 40 kt range over our eastern CWA border. H7 winds are
still a modest 20 to 30 kts across far western Colorado with 10 to
20 kts over the eastern CWA border. Given these winds and the deep
mixing expected, the chances of exceeding the 25 mph gust
threshold for Red Flag Warnings is high and the chances of max
temperatures exceeding guidance is also high. Therefore, went
ahead and upgraded the Fire Weather Watch to a Red Flag Warning
for all areas where fuels are deemed critical. It is Memorial Day
Weekend as well and confidence is high in this event occurring, so
felt it was prudent to upgrade with the morning package. Also
decided to extend the time of the Red Flag Warning to start
earlier at 10 am Saturday and end later at 10 pm Saturday. Winds
seem to get going a bit earlier than previously thought and RH
will be slower to recover Saturday evening, keeping the Fire
Weather threat elevated for a longer duration in some areas. High
clouds look to sneak in across the Front Range and divide late in
the day Saturday, but thinking this will be of the thinner
variety given overall lack of moisture depth and should still
allow for deep mixing regardless.

.LONG TERM...(Saturday night through Thursday)
Issued at 300 AM MDT Fri May 25 2018

There is no reason to string this out...chances of precipitation
with this next system are drying up like a lot of things in this
drought. The EURO`s rock solid consistency continues and now the
GFS is leaning more this way. If it continues, there should only
be some lighter precipitation associated with the back side of the
trough moving along the Wyoming border on Tuesday. Otherwise, it
looks as though the extended holiday weekend will be dry and just
slightly cooler with the thermal ridge axis pushing into the
Plains. In abnormally dry conditions, highs are often warmer than
guidance and we should stay some 5 to 8 degrees above late May
normals. The models are fairly consistent bringing some moisture
over the strengthening subtropical high by mid-week and this could
lead to an uptick in afternoon thunderstorms...or just virga and
wind since pessimism and persistence equals drought.


.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 300 AM MDT Fri May 25 2018

VFR conditions will prevail for the next 24 hours with a very slim
chance of any cloud cover across the region. Winds will be a
little breezy at times during the afternoon with well above
normal, near record warmth. Winds should remain breezy overnight
as a stronger low pressure system approaches the region by


Issued at 300 AM MDT Fri May 25 2018

A combination of hot, dry and breezy to windy conditions, in
addition to dry fuels, will lead to critical fire weather
conditions from late Saturday morning through Saturday evening.
Humidity values will drop below 15 percent in many valley
locations with a few spots dropping below 5 percent. Expecting
deep mixing up to 500 mb or higher where wind gust threshold of 25
mph should easily be exceeded across much of eastern Utah and
western Colorado. Therefore, the Fire Weather Watch has been
upgraded to a Red Flag Warning with the morning forecast package
for all zones where fuels are deemed critical.


CO...Red Flag Warning from 10 AM to 10 PM MDT Saturday for COZ200-202-



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