Scientific Forecaster Discussion
fxus65 kfgz 220344
Area forecast discussion
National Weather Service Flagstaff Arizona
844 PM MST Sat Sep 21 2019
Synopsis...expect another round of chilly overnight temperatures.
Sunday will feature dry weather and generally light winds. Showers
and thunderstorms are expected Monday through Wednesday. A few
stronger thunderstorms will be possible Monday afternoon and
Update...ideal radiational cooling conditions will lead to
another chilly night across northern Arizona. Expect low
temperatures to be similar to what we saw last night, with our
coldest high elevation areas dipping into the mid-upper 20s.
Sunday will feature continued quiet weather, with increasing highs
clouds through the day. Wind speeds will be weaker than we have
seen the past couple days.
Latest model guidance remains in good agreement on increased
shower and thunderstorm chances on Monday as remnant moisture from
Tropical Storm Lorena and an approaching disturbance interact.
Concern still exists for a few severe storms, especially Monday
afternoon and evening, with strong shear and enough instability
in place. Unsettled weather looks to continue through the
remainder of the week.
Lowered overnight temperatures 3-5 degrees in our cooler
locations such as Bellemont and the Grand Canyon with this update.
Otherwise, the forecast remains on track.
Previous discussion /229 PM MST/...another clear, sunny, comfortable
day has unfolded across northern Arizona. Temperatures are in the
mid 70s to 80s with afternoon breezes making for a very pleasant
afternoon. With dewpoints still in the single digits to teens with
overnight clear conditions, expect another very cool morning with
a few areas dropping near to below freezing. For Sunday, expect
similar fair and warm weather with afternoon breezes.
Starting Monday, we will see a change in the weather across the
area as an area of low pressure sinks in and interacts with
remnant moisture from Tropical Storm Lorena. Model trends are to
decrease precipitation amounts from previous forecasted heavy rain
event. However, model consistency from run to run is still
struggling to identify the final track of the low and swath of
heaviest precipitation causing low confidence on amounts and
locations. The 12z Euro began to come into somewhat better
alignment with the GFS on a more southerly and progressive track.
There is still moderate confidence that amounts of 1-2" with
locally higher amounts will be possible for areas south of the
Mogollon Rim over the period from Monday into Tuesday afternoon.
An additional thing to keep a close eye on for Monday evening into
Tuesday is the potential for some strong to severe storms. By
Monday afternoon, increased upper level flow will spread across
portions of Yavapai and Gila counties. This will provide better
wind shear to organize convection into the late afternoon/evening
Monday. This in combination with ample instability could result in
a few storms becoming severe. Be sure to check back in with the
forecast over the next 24-36 hours before making your Monday
Long term...Tuesday through Friday...there is fair agreement among
the forecast models through the remainder of next week. The closed
low moves into the southwest corner of Arizona Tuesday and slowly
meanders to the south and east through Wednesday. Northern Arizona will
remain on the northern fringe of the moisture and can expect to see
isolated to scattered showers or storms during this time.
Temperatures will be near to slightly below average.
The low is forecast to become absorbed into the mean flow and track
northeast across Arizona Wednesday night through Thursday bringing
another chance for some more organized showers and storms.
By Friday, as the aforementioned low heads east, a longwave trough
quickly develops across much of the western U.S. And remains in
place through next weekend. A low chance for showers will continue
through this time, but overall looks to be a cooler and windy
Aviation...for the 06z package...look for VFR conditions and
generally light surface winds at 5-15 kts over the next 24 hours.
Aviation discussion not updated for taf amendments.
Fire weather...expect dry weather and locally breezy afternoon
winds through Sunday. An area of low pressure approaching Arizona on
Monday will bring an increasing chance for showers and thunderstorms
through the day, lasting into Monday night. A few storms could
become strong. The best chance for wetting rains will be along and
south of the Mogollon Rim.
Tuesday through Thursday...unsettled weather continues with a
chance for showers and thunderstorms each day. Temperatures will
will remain near to a few degrees below normal.