Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/22/20
Area Forecast Discussion
National Weather Service Denver/Boulder CO
850 PM MDT Tue Apr 21 2020
.UPDATE...
Issued at 845 PM MDT Tue Apr 21 2020
Showers from Limon-Colorado Springs-South Park are gradually
fading. Colorado Springs wound up with the burst of evening
convection which should continue to drop southward. It`s possible
a few light snow showers will persist in the weak deformation over
the central mountains overnight, but it shouldn`t produce much
accumulation. Clouds should decrease over the northern areas as
weak convection wanes and the forcing sags slowly southward. Other
than minor adjustments for these trends...the forecast looks
good.
&&
.SHORT TERM...(This evening through Wednesday)
Issued at 222 PM MDT Tue Apr 21 2020
Scattered storms have developed and are pushing across the higher
elevations of the central mountains and portions of the eastern
plains mainly along and south of I-70 and I-76. Current ACARS
soundings show some weak dry intrusion that could keep the areas
further north on the plains more stable. Storms could produce
periods of light to moderate rain with gusty outflow winds,
lightning and maybe even some small hail with the stronger cells
into the early evening hours.
By midnight the models show the upper low pushing into the Texas
panhandle through the morning hours on Wednesday bringing flow
more northwesterly and increasing subsidence across the region.
This will help to bring any showers to an end with mostly dry
conditions across the region. There is a slight chance for some
isolated diurnal convection over the higher terrain by the
afternoon hours with light rain and lightning possible.
Temperatures will be some of the warmest of the week with highs
reaching into the upper 60s to lower 70s on the plains.
.LONG TERM...(Wednesday night through Tuesday)
Issued at 222 PM MDT Tue Apr 21 2020
A cooling trend with unsettled weather early in the extended period,
with the western US under northwest flow and a couple weak waves.
Ridge in the west builds late in the weekend, with warming
temperatures and dry weather into early next week.
Wednesday night begins with an approaching shortwave trough in the
NW flow and the leading edge of a 100+ kt jet making their presence
felt after midnight. With NW orographic flow and increasing RH have
increased pops a bit over guidance in the northern mountains per
collaboration with GJT and CYS. 100+kt jet core at 300 mb and weak
500mb trough with weak ascent in the QG fields pass through mid day
Thursday through Friday, with positive CAPE during the daytime and
best chances for precip during this time. Late Friday into Saturday
NW flow continues but absent organized lift pops begin to decline.
Sunday drier air moves in but still wouldn`t be surprised to see
lingering snow showers over the ridgetops. On the plains,
predominant northwesterly downslope flow will keep precip amounts
under a tenth of an inch, with a little boost from the terrain along
the Palmer Divide.
Upper ridge starts to build Saturday night, however a series of
northern stream troughs moves along the Canadian border, quashing
the ridge and keeping temperatures from warming to summer-like
levels, although they will still be above normal. Amplitude
increases for Tuesday with building heights and potential for warmer
temperatures. Dry through this period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 845 PM MDT Tue Apr 21 2020
VFR through Wednesday. A cold front will pass through Denver
12z-15z with north winds gusting in the 20-30 knot range behind
it.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Gimmestad
SHORT TERM...Bowen
LONG TERM...Hanson
AVIATION...Gimmestad
Area Forecast Discussion
National Weather Service Phoenix AZ
508 PM MST Tue Apr 21 2020
.UPDATE...Updated aviation discussion.
&&
.SYNOPSIS...
A weak disturbance moving through the state today will allow for
temperatures to be a few degrees cooler than yesterday. Breezy
conditions are also expected this afternoon as this disturbance
moves through. Much warmer conditions with high temperatures in
the 90s are expected for Wednesday into the weekend as a strong
ridge of high pressure aloft builds in over the region. Lower
desert high temperatures will approach 100 degrees over the lower
deserts by Friday or Saturday with lower 100s likely by Sunday
into early next week.
&&
.DISCUSSION...
A weak closed low is moving southeast into northern Arizona this
afternoon. This feature will continue to weaken as it quickly moves
away from the forecast area tomorrow. Winds will increase this
afternoon, with gusts of 20-30 mph common across most of the lower
deserts. Temperatures this afternoon are also a few degrees cooler
than yesterday, with most lower desert locations in the upper 70s
and lower 80s this afternoon. Showers and thunderstorms are
generally expected to remain north of the Maricopa County line
this afternoon given a relative lack of moisture and a stout
inversion near 600 mb evident on aircraft soundings into PHX.
However, a rogue shower or two may clip northern portions of the
county, with weak northwesterly and northerly outflows moving
into at least far northern portions of the Phoenix metro over the
next couple of hours from a dissipating shower moving into Sun
City now and a stronger pair of thunderstorm cells located north
and northwest of Black Canyon City. These outflows will be similar
to or weaker than the 20-30 mph westerly gusts currently ongoing
across south central Arizona this afternoon, with weaker gusts
over southeast California and south central Arizona. Wind gusts
will subside tonight, setting up light diurnal winds under clear
skies overnight with lows in the upper 50s to lower 60s.
The main story for tomorrow into the weekend and beyond will be
increasing temperatures as a strong upper level ridge builds over
the eastern Pacific. As this area of high pressure strengthens
and progresses eastward toward the western CONUS, it will promote
dry anti-cyclonic northwesterly flow aloft over the region,
allowing for skies to remain clear to mostly clear. Daytime
temperatures will climb into the low to mid 90s starting tomorrow,
with temperatures climbing through the rest of this week. By
Friday or Saturday, ensemble guidance shows near record high
temperatures across lower desert locations approaching 100
degrees as the upper level ridge begins to shift inland, with
lower 100s forecast by Sunday. NAEFS percentiles show H5 heights
climbing above the 90th percentile over Arizona this weekend, with
ensemble model clusters generally in agreement that strong upper-
level ridging will persist over the Southwest into next week.
Regardless, it appears that the Phoenix metro will likely see its
first day above 90 degrees tomorrow with our first 100 degree day
within a few days of that. This has only occurred four times
since 1896, which includes the following:
Year (# of Days) Dates (Temperatures)
1994 (1)April 15th (92) and April 16th (100)
1988 (3)March 23rd (90) and March 26th (100)
1984 (4) April 12th (90) and April 16th (101)
1946 (6) April 11th (97) and April 17th (100)
As you can see above, none of these years had their first 90
degree day quite as late as this year. Assuming tomorrow is our
first 90 degree day, that will be our latest first 90 degree day
since 1995 (which was on April 26th) and more than three weeks
behind our average first 90 degree day of March 31 (based on the
1981-2010 period). Our average first 100 degree day for the
1981-2010 period is May 2nd, so we will only be about a week ahead
of schedule for that. The forecast for the second half of next week
becomes a bit more uncertain as many ensemble members show a weak
trough pushing into the western U.S. that should eventually cause
a slight decrease in heights and temperatures aloft. The ECM
ensemble`s preferred cluster is a bit more progressive than the
GEFS which depicts a stronger ridge centered over the Great Basin
and the Canadian which is a mix between the two. Regardless, above
normal temperatures are expected next week, with these model
variations making the difference between upper 90s and mid 100s.
&&
.AVIATION...Updated at 0007Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
A southward-moving outflow continues to push through the metro
late this afternoon. Strongest winds are along I-17. The outflow
is already through KDVT and KSDL and should reach KPHX shortly
after 00Z and KIWA around 01Z. Northerly wind gusts up to 20-25
kts will be possible with this outflow at KPHX and likely weaker
at KIWA. An hour or so following the outflow, winds may shift back
towards the west briefly and possibly even become variable,
before shifting easterly and weakening significantly by 6-8Z SCT
CU should clear over the next couple of hours and remain clear
through Wednesday morning. FEW CU will likely develop over high
terrain again Wednesday afternoon. Winds will shift westerly by
17-18Z Wednesday with afternoon gusts to around 20 kts.
Southeast California/Southwest Arizona including KIPL and KBLH:
Clear skies will prevail through the TAF period. Light westerly
winds are favored tonight through Wednesday morning at both
terminals and then veer northerly Wednesday afternoon. Wind gusts
Wednesday afternoon up to 20 kts at KBLH, with lighter winds,
generally 10 kts or less, at KIPL.
&&
.FIRE WEATHER...
Friday through Tuesday: Much warmer temperatures are expected as
high temperatures over the lower deserts increase into the upper
90s to near 100 degrees by Friday and Saturday, with lower 100s
expected by Sunday into early next week. Minimum relative
humidity values will fall to near 10 percent on Friday with single
digit values over the weekend into early next week. Relative
humidity levels will recover into the 20-30 percent range each
night with higher values after Sunday over far southwest Arizona
and southeast California due to weak Gulf surges. Winds will
generally follow diurnal tendencies and remain light through the
period aside from brief afternoon gusts under high pressure aloft.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hopper/Hodges/Smith
AVIATION...Benedict
FIRE WEATHER...Hopper/Smith
Area Forecast Discussion
National Weather Service Great Falls MT
756 PM MDT Tue Apr 21 2020
.SYNOPSIS...
After another mild and breezy day is expected on Wednesday, with
increasing precipitation chances over the mountains Wednesday
afternoon and then over the plains and valleys Wednesday evening.
Temperatures will cool some 5 to 15 degrees for the day on
Thursday, with continued chances for lower elevation rain showers
and mountain snow showers. A few thunderstorms are even possible
during the afternoon hours on Thursday.
&&
.Evening Update...
Update has been published, with primary adjustments made to
hourlies to account for latest trends and observations. Otherwise,
made some tweaks to MaxRH`s for tonight, mainly to push values
higher in the valleys of Southwest and Central Montana where I
expect the boundary layer to decouple during the overnight hours.
This has led to the addition of some patchy fog in the Hebgen, Big
Hole, Smith Valleys (to name a few) during the early morning hours
on Wednesday. Outside of the patchy fog in the aforementioned
areas, a few sprinkles/isolated showers can`t be ruled out along
the Northern Rocky Mountain Front and Hi-Line this evening/early
Wednesday morning as a weak shortwave exits the region. - Moldan
&&
.AVIATION...
Updated 609 PM MDT Tue Apr 21 2020 (22/00Z TAF Period)
The 22/00Z TAFs begin with VFR conditions at all airfields. Toward
the end of this TAF period, expect precipitation to begin at KGTF
and the southwest airfields, causing conditions to fall into the
MVFR range. Additionally, mountain obscurations are forecast.
Aircraft icing will impact aviation, at times. Periods of gusty
winds can be expected, with LLWS forecast at KLWT. Expect the
associated TURBC.
- Fogleman
NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing
runway closure.
&&
.HYDROLOGY...
Flood watches continue for portions of Hill and Blaine counties
for the foreseeable future. Temperatures across North Central
Montana and Southern Alberta/Saskatchewan today have risen into
the upper 60s to low 70s, which combined with breezy winds and
abundant sunshine is leading to increased snowmelt in the Bears
Paw Mountains and Cypress Hills. Additional snowmelt is expected
throughout the overnight hours as temperatures remain mild and
above freezing. This snowmelt and subsequent runoff into local
waterway could result in quickly rising creek levels on both
Clear Creek and Lodge Creek. Persons with interest along these
and any other creeks emanating from the Bears Paw Mountains and
Cypress Hills should remain alert for rising water levels. -
Moldan
&&
.PREV DISCUSSION...
/ISSUED 609 PM MDT Tue Apr 21 2020/
Rest of this afternoon through Friday...primary concerns throughout
the period will be precipitation chances and type.
Broad upper level ridging was in place across the western 1/3rd of
the CONUS and Canada this afternoon, with the ridge axis extending
north northeast from just off the California Coast, to North Central
Washington, to the British Columbia/Alberta borders. A weak wave
embedded within the downstream side of this ridge was sliding
southeast over the Northern Rockies this afternoon, which was
leading to some increases in low to mid-level cumulus clouds and
breezy surfaces winds due to efficient mixing of the mid-level
winds. A few rogue showers/sprinkles could materialize late this
afternoon and evening along the Hi-Line and Northern Rocky Mountain
Front due to aforementioned shortwave moving over the region, but
any precipitation amounts would very light. Breezy surface winds
during the overnight hours across Central and North Central Montana
will once again help to keep temperatures above climatological
norms (generally in the upper 30s to low 40s), with more seasonable
temperatures across Southwest Montana where the boundary layer is
expected to become decoupled.
By Wednesday, the upper level ridge across the Western CONUS/Canada
will begin to be broken down and flattened-out as shortwave moves
from the Pacific Northwest (Wednesday morning/early afternoon) and
over the Northern Rockies (late Wednesday afternoon/early Wednesday
evening). This shortwave will bring increasing chances for mountain
rain/snow showers and valley/plains rain showers for the day on
Wednesday. As the shortwave continues to slide east southeast and
away from the region Wednesday night, northwest flow aloft will
develop over the Northern Rockies and persist into the day on
Friday. This moist and unstable flow will once again support
scattered to numerous showers across the region on Thursday, with
even the chance for isolated to scattered thunderstorms. With snow
levels across Southwest, Central, and North Central Montana hovering
between 5500-6500ft from Wednesday through Thursday night and a high
April sun angle, am not expecting much in the way of impacts to
transportation over mountain passes (outside of refreezing roads
during the overnight hours). Biggest impacts from this storm will be
the fact that this will likely be the first appreciable rainfall
(0.10" or greater) on top of the remaining snow in the mid-slopes,
which could lead to increased runoff into local streams/creeks, in
addition to weakening the stability of the snowpack and raising the
danger for wet avalanches. - Moldan
Saturday through Next Tuesday...
A period of transitory upper level ridging looks to shift east
across the region early this weekend before the next round of
Pacific energy moves across the region late in the weekend into
early next week. We should see at least one day of warm and dry
conditions this weekend before conditions turn unsettled and
slightly cooler again, though there are some discrepancies still
at this point on when the next round of energy arrives. - Hoenisch
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 41 66 41 57 / 0 20 40 70
CTB 40 61 38 56 / 0 10 10 50
HLN 41 66 40 57 / 0 20 40 80
BZN 32 66 39 55 / 0 30 60 90
WYS 22 51 31 48 / 0 30 70 90
DLN 35 61 38 53 / 0 10 20 80
HVR 44 68 43 61 / 0 10 40 30
LWT 37 63 38 52 / 0 10 50 60
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
Flood Watch from Wednesday afternoon through late Sunday night
Blaine...Hill.
&&
$$
http://www.weather.gov/greatfalls