Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus65 kgjt 231725 
afdgjt

Area forecast discussion
National Weather Service Grand Junction Colorado
1125 am MDT Mon Sep 23 2019

Short term...(today through tuesday)
issued at 412 am MDT Mon Sep 23 2019

High clouds are seen streaming across the area from the southwest
and will continue to do so as a low pressure trough over the
Pacific northwest drops southward through the Great Basin today.
Warm air advection will occur out ahead of this low across our
area in southwest flow, resulting in dry and breezy conditions at
times this afternoon. The winds lessen late in the day as the low
drops further south through Nevada and Southern California,
arriving to the northern baja in Mexico by Tuesday. Some isolated
storms are possible across the extreme south near The Four Corners
but confidence is low that anything will actually occur. This low
will close off over northern Mexico and take a vacation, spending
its time on the shores of the baja through Thursday. Storms will
favor the right front quadrant of this upper low, with Arizona
being the Focal Point for convection on Tuesday. On the western
slope, we will remain underneath a deformation zone as this low
splits off the northern branch of the upper level jet, with dry
and warm conditions and light winds. Temperatures will be above
normal both today and Tuesday to welcome in the fall season.

Long term...(tuesday night through sunday)
issued at 412 am MDT Mon Sep 23 2019

Dry conditions and warm, above normal temperatures continue
Wednesday and Thursday as the low slowly meanders from northern
Mexico into southwest Arizona by Thursday. This low will weaken as
it tracks northeast through Arizona on Thursday and opens up,
becoming absorbed in the mean flow from the northern branch of the
jet. 700 mb temps warm to +12c to +14c by Thursday afternoon and with
precipitable water (pw) values less than 0.6 inches across much of
the region with exception of The Four Corners, anticipating a much
drier day than earlier anticipated. All model solutions have
really backed off on pops, holding off until Friday when the
trough actually moves through the area. So, in coordination with
surrounding offices, drastically cut back on pops Thursday through
Friday morning from what the blended solution gave. Still have
some isolated storms Thursday afternoon over the San Juans mainly
as there may be a few in the warm advective southwest flow due to
lift from terrain and diurnal heating.

The low opens up and weakens as mentioned earlier, moving south of
The Four Corners through northern Arizona and northern New Mexico
during the day on Friday. This will result in an increase in
showers and storms with the best chance of precipitation occurring
as this trough gets absorbed and pushed along by the active
northern stream. Trended pops in this direction to increase
slightly Friday morning with peak period Friday afternoon into the
evening.

Looking towards the weekend, this is where the model consistency
drops off even more so. Overall, the models agree that a large
trough will get carved out over the Pacific northwest upstream on
Saturday and deepen over the Great Basin Sunday heading into early
next week. The GFS indicates a dry slot happening with the
gradient tightening resulting in a dry, windy and warmer day on
Saturday. 700 mb winds increase to 30 to 40 kts Saturday and Sunday
with the upper level jet of 100 kts overhead. 700 mb temps also
increase towards +10c to +12c. The European model (ecmwf) on the other hand is more
aggressive with the moisture showing more storm coverage focused
over high terrain. If the GFS is correct, we could see
temperatures exceeding guidance and potential for critical fire
weather conditions. However, the blended solutions seem to be
holding on to a bit more moisture, resulting in higher relative
humidity values and greater coverage of pops. Did bump up the Max
temps a bit over the weekend but left pops as is as it was showing
isolated to scattered mainly over high terrain which seemed
reasonable given model differences. This is still a ways out but
just tossing out the range of solutions and potential the forecast
could change quite a bit over the next few days.

&&

Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 1116 am MDT Mon Sep 23 2019

VFR conditions will prevail at all terminals today. High clouds
will continue to stream in from the south over dro and tex however
ceiling heights will remain well above ils thresholds. Expect
continued cloud cover overnight into Tuesday morning near The Four
Corners with mainly clear skies at all other terminals. VFR will
dominate area wide again on Tuesday.

&&

Gjt watches/warnings/advisories...
Colorado...none.
Utah...none.
&&

National Weather Service Glossary of Abbreviations