Scientific Forecaster Discussion
fxus65 kfgz 161639
Area forecast discussion
National Weather Service Flagstaff Arizona
939 am MST Mon Sep 16 2019
Synopsis...moisture will remain in place across northern Arizona
today as a low pressure system moves into the Great Basin. The
result will be a chance for showers and thunderstorms through
this evening, along with strengthening southwest winds. Drier and
breezier conditions are forecast for Tuesday and Wednesday.
Update...the trough moving onto the West Coast this morning
continues to pull low-level moisture northward into central and
northern Arizona. Some isolated shower and thunderstorm activity
is already developing from around Prescott up to near Williams and
Bellemont. Still expecting storm coverage to increase into the
afternoon and early evening, with the highest coverage along/east
of a Prescott to Flagstaff to Four Corners line. Best instability
is forecast over Gila and southern Yavapai counties where a few
stronger storms with hail and gusty winds could develop. Winds at
the surface and aloft have increased this morning, and storms will
be moving toward the northeast at around 20 mph.
Previous discussion /352 am MST/...satellite indicates mid-level
clouds from about I-17/US 89 westward, with an area of lower
clouds near the New Mexico state line. Surface observations and
adot web cameras are indicating just lower clouds with no
appreciable fog, but patchy fog has been added to a few spots in
eastern Arizona through 8 am MST just in case it develops as the
low clouds dissipate.
For today...Storm Prediction Center mesoanalysis indicates an area of instability
across much of Yavapai County at present. Hi-res models indicate
the possibility of a few storms over this area through the
morning. Coverage of showers and storms is expected to increase
to the north and east after about noon, with some training storms
possible given the increase in southwesterly winds.
Tuesday and Wednesday...href mean quantitative precipitation forecast is much less on Tuesday than
on Monday, with a few storms possible in the afternoon but fairly
weak in nature given the expected drying. Southwest wind gusts to
around 35 mph are forecast along the Mogollon Rim and Coconino
Plateau on both Tuesday and Wednesday as another low pressure
system drops from the Pacific northwest into the Great Basin.
Temperatures will be near to slightly above normal.
From Thursday Onward...the strongest winds of the week are
forecast for Thursday with gusts in excess of 40 mph expected,
along with a chance for precipitation especially in eastern
Arizona. Cooler temperatures are expected Thursday as the trough
gets closer. Friday through Sunday, a general westerly flow is
expected with some weak disturbances perhaps moving through. Frost
and even some local freezing temperatures will be possible at high
elevations through this period. Low rain chances appear again
toward the early part of next week.
Aviation...for the 18z package...isolated to scattered rain showers/thunderstorms and rain
are expected through this evening with the higher coverage
along/east of a kprc-kflg-kov7 line. Gusty winds to 35 kt and
decreased visibility near the strongest storms. Otherwise, VFR
conditions are forecast through 18z Tuesday. Aviation discussion not
updated for taf amendments.
Fire weather...moisture will remain over northern Arizona today with
a chance for showers and thunderstorms during the afternoon and
evening. Southwest winds will increase from today into Tuesday which
will promote drying. Much lower storm coverage is expected on
Wednesday through Friday...near critical fire weather conditions
will be possible across portions of northwestern Arizona Wednesday
and Thursday due to gusty southwest winds and low relative humidity.
A chance of precipitation returns Thursday to mainly eastern Arizona.