Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/26/17
Area Forecast Discussion
National Weather Service Green Bay WI
517 PM CST Sat Feb 25 2017
Updated aviation portion for 00Z TAF issuance
.SHORT TERM...Tonight and Sunday
Issued at 224 PM CST Sat Feb 25 2017
The latest RAP analysis and satellite/radar imagery show a large low
pressure system continuing to exit the region over northwest Quebec.
Cloud cover, snow showers, and flurries wrapping around the low are
persisting early this afternoon over north-central and eastern
Wisconsin. The back edge of the clouds are pushing into western
Marathon and Wood counties, and should exit northeast Wisconsin by
late this afternoon or early this evening. Looking to the west, a
corridor of clearing has moved into western Wisconsin and eastern
Minnesota in close proximity to a surface ridge axis. The next
system, however, is already diving southeast across the northern
Plains with scattered snow showers over North Dakota and northern
Minnesota. Forecast concerns revolve around cloud trends this
afternoon, followed by snow shower chances late tonight into Sunday
with this next system.
Tonight...A weak surface ridge axis will pass across the area and
provide a brief period of clearing during the first half of the
evening. Then will see increasing clouds again from the west as
warm advection pushes in aloft ahead of a weak shortwave. Saturation
looks deep enough over north-central and central WI for a chance of
snow showers overnight, but not expecting much in the way of
accumulations. With cloud cover and a tight pressure gradient, low
temps should not fall much, and will go with lows in the teens.
Sunday...That shortwave will slide across the area while pushing a
cold front into central and north-central WI. The front looks
relatively sharp with decent convergence that will provide a focus
for snow shower development with heating of the day. Would not be
surprised if a few snow showers become briefly heavy given mid-level
lapse rates around 7 c/km. Up to an inch of snow looks possible
over Vilas county. Chances of snow showers are less over eastern
Wisconsin but dont think can rule them out with passage of the
shortwave and aforementioned lapse rates. High temperatures will
rise to near 30 degrees in the north, to the middle 30s south and
.LONG TERM...Sunday Night Through Saturday
Issued at 224 PM CST Sat Feb 25 2017
A weak ridge near the surface will help keep the area dry Sunday
night and into Monday night, ahead of an approaching surface low
with associated upper level trough.
As precipitation enters the region, a brief period of wintry mix
is expected to move across areas of northern Wisconsin while rain
remains the primary weather type towards the Fox Valley. As warm
air advection takes over near the surface in the mid to late
morning, rain will overspread the remaining areas in the north. A
slow switch back to snow is anticipated in the evening. This
transition will spread north to south as weak cold air advection
filters in behind this system. A brief break in the action is
expected as some dry air works its way in the back end of this
system in the early morning Wednesday before another shortwave
comes through to fill in some additional snow shower chances for
Wednesday morning to afternoon. A brief clipper system is still
expected to follow Thursday as northwesterly flow dominates,
bringing additional snow chances mainly to the northern areas.
Weak lake effect snow signals then linger on into next weekend.
A warming trend is expected ahead of the trough through Tuesday as
temperatures rise to well above normal, followed by a slow
cooling trend back to near normal by Thursday. Northwesterly flow
into the weekend will then bring temperatures to a few degrees
below normal by Saturday.
.AVIATION...for 00Z TAF Issuance
Issued at 517 PM CST Sat Feb 25 2017
A brief period of clearing will track through the region this
evening, before additional clouds arrive from the west ahead of a
weak clipper system. These clouds should lower overnight into low
mvfr range over central and north-central WI, with potential for
scattered light snow flurries/showers. Scattered snow showers will
likely persist across northern Wisconsin for much of Sunday with
arrival of a cold front, and possibly push into the Fox
Valley/Lakeshore areas during the morning. IFR visibilities will
be possible within any snow showers.
Area Forecast Discussion
National Weather Service Phoenix AZ
859 PM MST Sat Feb 25 2017
Slightly cooler than average temperatures will persist through
early next week as two fast moving weather disturbances move into
the region Sunday, then again Monday night and Tuesday. The
weather system Monday night and Tuesday will have best potential
for spreading rain across the area. Dry conditions and much warmer
temperatures will return by the middle of next week.
Latest water vapor imagery shows a well-defined vort max at the
base of a short-wave trough across the northern California coast
extending eastward into the intermountain West. However, there is
little precipitation to show for it at the present time. Latest
model guidance continues to indicate that mid and high clouds will
stream across the forecast area tonight. Most recent runs of the
HRRR suggest conditions will continue to moisten in the lower-
levels of the atmosphere late Sunday morning and early afternoon
for a few showers across the lower deserts. However, any rain that
develops is expected to be brief and light. In the short-term,
only minor adjustments were needed to the temperatures and
dewpoints. Otherwise, the forecast remains on track.
High clouds continue to stream eastward across southern and
central California within predominantly westerly flow established
over the Southwest. Slightly below-normal temperatures will
continue today and tomorrow as midlevel heights remain suppressed
with an active storm track to the north. A series of upstream
shortwave troughs, noted as two features evident on water vapor
off the northern California coast and near the Alaska Panhandle,
respectively, will move through the region through mid-week. The
first will be a fast-moving system that will deamplify while
rapidly moving eastward tomorrow. Forcing for ascent associated
with this feature will be rather focused, and could produce some
showers across central and northern portions of Arizona, but the
lack of moisture will limit the potential for any widespread or
substantial precipitation. Slight chance PoPs exist tomorrow
morning and afternoon across roughly the northern half of the CWA,
including the higher terrain of Maricopa and southern Gila
counties, and Joshua Tree National Park. An increase in mid-to-
high-level clouds is also expected.
Attention then turns to a more substantial upper trough which will
deepen along the Pacific coast through Monday. This feature will
phase with a narrow southern stream plume of moisture, and bring
increased rainfall potential beginning late Monday and Tuesday.
Similar to the last major system, the trajectory of the preceding
moisture plume should favor the most widespread precipitation
across central and northern portions of Arizona through early
Tuesday, before shifting into eastern Arizona by late Tuesday. As
a result, PoPs have been adjusted upward again for Monday evening
and Tuesday. QPF amounts have also been increased to be more in
line with the latest WPC guidance, with roughly 0.5-1 inch
expected from near Phoenix and areas to the north/east. A few of
the higher elevation locations may locally receive over one inch
of rain. Given the orientation of the moisture plume relative to
the positively tilted system, snow levels should remain high
enough to preclude snowfall over the higher elevations of southern
Gila and northeast Maricopa counties. A second, drier disturbance
is forecast to move through the area Wednesday, but will be
moisture-starved, before more substantial midlevel ridging builds
over the western CONUS and ushers in a return of above-normal
temperatures and dry conditions late next week.
South-Central Arizona including KPHX, KIWA,and KSDL:
Southeast California/Southwest Arizona including KIPL and KBLH:
A low pressure system centered off the northern California Coast
will weaken as it moves inland. It will spread increasing
cloudiness over the forecast area from west to east tonight
through Sunday morning with ceilings getting progressively lower.
However, anticipate ceilings to remain above FL080. There will be
a lot of virga with some spotty very light showers/sprinkles
reaching the ground (mainly after 10Z over southeast CA and after
14Z over south-central AZ). Westerly winds aloft will strengthen
with the passage of this system. Westerly surface winds will
strengthen over southeast California tonight with occasional gusts
of 20-25 kts (especially over, and west of, the Imperial Valley).
Those breezes will slowly expand eastward during the day Sunday.
Aviation Discussion not updated for amended TAFs.
Monday through Friday...
A Pacific low pressure system will bring good chances of wetting
rains mainly Monday night through Tuesday morning focused
especially across the high terrain of Arizona. Below normal
temperatures are expected through next Wednesday with a
significant warming trend likely late next week. Breezy conditions
for Monday and Tuesday are expected in most areas with breezy
conditions persisting down the Lower Colorado River each afternoon
through at least Thursday. Increased humidities with minimum
readings between 25 to 35% through Tuesday will dry out starting
Wednesday with afternoon readings closer to 15% over the deserts
for Wednesday through Friday.
.SPOTTER INFORMATION STATEMENT...
Spotter reports will not be needed through the weekend.
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