Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/02/21

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
301 PM AKST Mon Feb 1 2021 .SHORT TERM.../Monday and Tuesday/ A very complex and dynamic winter storm continues to unfold across Southeast Alaska this afternoon as a developing area of low pressure moves SE out of the northern gulf. Heavy bands of snow continue to move through the northern half of the Panhandle this evening as seen on satellite and radar imagery. Lower resolution models struggle with identifying mesoscale features and their evolution through time; making forecasting bands of heavy snow very difficult more than a few hours out. Guidance over the past few days has been indicating a convergence zone setting up over the Central Panhandle where a heavy snow band would likely develop; however lower confidence existed on the exact location it would form. Guidance last night trended the placement of this band further west and model runs today continued that trend. What looked to be a Kake snow event yesterday has turned into a Juneau to Angoon to Little Port Walter snow storm as the narrow band of heavy snow has set up right over this area. 12z RAOB soundings and recent MDCRS soundings indicate a stable boundary layer with NE winds keeping cold air at the surface with a very unstable layer above 850mb and into the DGZ. Mid and upper level lapse rates exceeding 8.5C/km and a fully saturated column indicate efficient snowflake production in the DGZ, high snow to liquid ratios, and the possibility for impressive snowfall rates of 1-2" per hour. This morning, Yakutat received 8-10 inches of snow within a 10 hour period with only 0.25 inches of liquid, yielding snow ratios upwards of 40:1! With the banded and showery nature of the snow, snow accumulations will greatly vary from one town to the next. Under the heavy snow band across the north central Panhandle, expect an additional 3-6 inches through this evening with snowfall rates exceeding 1" per hour. The Winter Weather Advisory for Juneau and Angoon has been upgraded to a Winter Storm Warning as total snow accumulations through tonight will be upwards of 4 to 9+ inches. Lower, sub advisory snow amounts expected around Haines, Gustavus, Pelican, and across the southern half of the Panhandle. As the area of low pressure moves SE along the coast, expect precipitation to pivot and sag southward along the Outer Coast. Guidance has also trended a tad further west with the position of the low, keeping the heaviest snow slightly offshore of POW Island. Kept slight chance to chance wording for POW Island as a few snow showers will still be possible through Tuesday morning. A northerly outflow event begins as this system departs tonight and into Tuesday. Storm force northerlies develop in Lynn Canal with small crafts in the Central Inner Channels on Tuesday. Expect gusty winds to 50 mph in Skagway during this time frame as well. Mountain Wave guidance indicates marginal conditions for Taku Wind development late tonight through Tuesday morning. Currently do not expect a full Taku to develop; however with a strong northerly gradient, gusts to 40-50 mph are still possible in Downtown Juneau and Douglas. Along the Northeast Gulf coast, expect gale force winds blowing out of interior passes. Confidence is only around average for the short term as the main challenge will continue to be pin pointing exactly where smaller snow bands set up Monday evening. .LONG TERM.../Wednesday through Monday night/...Extended forecast period begins with a broad ridge to the south. Northwesterly flow will be in place behind a low that has departed to the southeast and will promptly be replaced by another low and associated frontal system. A very tight pressure gradient through the northern inner channels will be slackening at the beginning of the forecast period as well. Overall, the region should be cold enough for the predominant precip type at the onset for this Wednesday system to be snow, however, flow will switch around to the south and should see a transition to rain early for most coastal areas and the southern inner channels. Through the inner channels, early indications are that this warm push should be able to transition precip over to liquid as far north as Hoonah before the end of the day. Precip associated with this system should linger through Thursday for many areas and by the end of day two, may see the change over to rain reach Gustavus and Juneau. Snowfall totals from this system look to be mostly unimpressive for southeast with the exception being the interior location of Hyder which remains cold enough for snow and gets the added benefit of the highest precip totals being in the southern panhandle. Any break that we get from precip should be short lived as the pattern remains active with yet another front poised to impact the region from the southwest Friday into Saturday. Noticeably warmer air can be expected with this front. How far this can actually drive the rain/snow line north is still up for a great amount of scrutiny, but what is becoming increasingly evident is that Haines and Skagway do not look likely to see much of that warm up and with the amount of moisture that could be accompanying this front, a decent snow event may be in the works. For the duration of the forecast, a sizable break in precipitation does not appear to be in the cards as the Fri/Sat front is projected to trough out over the region before being absorbed into yet another frontal system late in the period. By this point, enough "warmer" air may have crept into the region, and with persistent cloud cover, diurnals may not be in play which could lead to less likelihood for snow for many areas, or the alternative of temperatures fluctuating right around the freezing mark. Still have plenty of time for future analysis regarding such things, but for now, optimistically wishing for the warm up. && .AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...Winter Storm Warning until 11 PM AKST this evening for AKZ024- 025. Strong Wind from 9 PM AKST this evening through Tuesday morning for AKZ025. Strong Wind until 6 PM AKST this evening for AKZ018-019. Strong Wind from midnight AKST tonight through Tuesday afternoon for AKZ019. Winter Weather Advisory until midnight AKST tonight for AKZ021. Strong Wind from late tonight through Tuesday afternoon for AKZ018. Wind Chill Advisory from 3 AM Tuesday to 6 AM AKST Wednesday for AKZ018. MARINE...Heavy Freezing Spray Warning for PKZ011-013. Heavy Freezing Spray Warning for PKZ012. Storm Warning for PKZ012-013. Gale Warning for PKZ021-022-031-032-043-051. Small Craft Advisory for PKZ011-033-034-041-042-052-053. && $$ CM/JDR Visit us at
Area Forecast Discussion
National Weather Service Phoenix AZ
415 PM MST Mon Feb 1 2021 .UPDATE... Updated Aviation && .SYNOPSIS... Strong high pressure developing across the region will allow for continued warm temperatures through Wednesday, despite considerable cloudiness. High temperatures across the lower deserts should top out in the mid to upper 70s during this time. A weather system is then expected to move through the region late Wednesday into Thursday with the best chances for precipitation across the Arizona higher terrain and only slight chances across the lower deserts. After a brief cool down Thursday into Friday, temperatures are likely to slowly warm back up. && .DISCUSSION... Widespread and dense cloud cover has overspread the area due to moist southwesterly flow. This is being driven by a deep trough off the west coast which is slowly moving southeast. ACARS soundings reveal a moist airmass above about 700 mb, but very dry and stable air below that. Higher pressure to the northeast over the Great Basin has resulted in breezy easterly conditions for portions of Phoenix today as well. Meanwhile, a high amplitude ridge remains over Arizona with very warm temperatures aloft. However, due to the clouds and low level cooler air surface temperatures will remain stable the next few days, with highs in the mid to upper 70s. However, should the clouds be somewhat thinner than anticipated temperatures could be a bit warmer. For instance, NBM temperature probabilities show a 40-45% probability of reaching 80F on Tuesday, and a 25-30% probability of reaching our daily record high of 82F. This would reflect an outcome with lower than expected cloud cover. The high amplitude ridge will begin to break down on Tuesday as the previously mentioned trough moves into the area. As it does so,the trough will split, with decent agreement that the southern lobe will stall well southwest of the California coast for several days. The northern branch of the trough will clip the four corners region. WPC cluster analysis shows some variations in the amplitude of the clipper system, which would result in cooler high temperatures should the trough end up more amplified. Even in the cases of the more amplified trough, very few ensemble members produce any precipitation for Phoenix. If these wetter solutions verify, total precipitation would still be negligible. As commonly occurs with these systems, higher pressure will build north of the area and result in breezy northerly winds Wednesday night through Friday. The strongest of these winds will be in the Colorado River Valley and along the foothills north and east of Phoenix. For the upcoming weekend, the ensemble cluster analysis has transitioned toward the high amplitude ridge building off the West Coast late this week being more of a factor for our region by Saturday or at the latest Sunday. This is now leading to higher confidence in warming taking place during the weekend and possibly into early next week. There is still a good amount of spread within temperature guidance, but it is looking more likely we will be seeing a return to above normal temperatures by early next week. Rain chances will remain minimal through this period. && .AVIATION...Updated at 2315Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: No significant weather issues will exist through Tuesday evening as thick cigs varying in a 12K-20K ft range gradually break through the period. While virga and perhaps a sprinkle will be common this evening, no accumulating rainfall is expected. Otherwise, east winds will prevail much of Tuesday with moderate confidence a light west wind will develop through mid/late afternoon. Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist as thick 12K-15K ft cigs eventually scatter throughout the day Tuesday. While a light N wind will be preferred at KBLH and NW component at KIPL, extended periods of light and variable winds will be common. && .FIRE WEATHER... Wednesday through Sunday: Wednesday will remain quite warm before an approaching weather system brings a brief period of cooler temperatures late in the week. The next weather system will bring chances for wetting rains mainly be across higher terrain areas of eastern and central Arizona late Wednesday into early Thursday. Generally dry conditions are then expected Friday through the upcoming weekend. Winds early in the period will be breezy at times, especially across the Lower CO River Valley, while lighter winds are expected Friday through Sunday. Minimum RHs on Wednesday and Thursday across Arizona will mostly be around 25% before dropping into a 15-20% range by Friday. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ DISCUSSION...Hodges/Kuhlman AVIATION...MO FIRE WEATHER...Kuhlman