Nov 27: Thanksgiving Forecast

Nov 27: Thanksgiving Forecast

Written on 11/27/2019
Jonathan Carr

Discussion: Let’s first address tonight and Thanksgiving (tomorrow). A fairly organized low pressure system will tracking to our N (from W to E). It looks like it makes a run from the Great Lakes over N New York State and then ultimately over Maine while fluctuating between about 989mb and 995mb. New Jersey will see a cold front, attached to the S side of this low, push through between this evening and early Thanksgiving morning. Frontal precipitation is not a big deal and should fall between now and midnight tonight. Once the cold front is through we should feel a cold and dry Thanksgiving day with strong winds rocking from W/NW to N throughout the day. You might even see some lake-effect/remnant moisture flurries tomorrow but no accumulations or disruption. Again, I see problems with the NYC parade balloons but that’s a separate conversation. The N flow then holds and keeps us chilly through late-Sunday morning.

Now let’s address the latest about the weekend coastal storm system. The one major trend I’ve noticed is the overall timing of the precipitation window. It is now between Sunday morning and Monday evening no longer between Saturday night and Monday morning. So timing has pushed a little to the right. However we are still expecting three phases of the system:

Phase 1: The SW Flow. This is a more confident part of the forecast. High pressure to our N/NE will be pumping cold in at the surface as warmer air advects at the low-mid levels above it from the SW. This gives us overrunning precipitation over the warm front that will fall through the colder surface levels. This means a snow to ice (sleet/freezing rain) to rain situation is possible especially NW of the NJ Turnpike. The traditional colder elevations of NWNJ have the best chance to see an inch or two of snow before the changeover. The ice threat is a little more serious and is a valid concern for everyone along and NW of the NJ Turnpik. Areas SE of the NJ Turnpike will likely start as rain or see a very quick changeover should they start wintry. This phase is now expected for Sunday morning through early Sunday afternoon.

Phase 2: Coastal Storm Development. This phase is the most confident part of the forecast. The primary low will be driving into the Great Lakes area during phase 1. It will then transfer to a secondary low somewhere off the coast of Delmarva/New Jersey. During this transfer all of New Jersey likely goes over to all plain rain and winds will pick up either right off the ocean (E/NE) or possibly just NE. Either way this hurls warmer marine air over all of New Jersey and torches any wintry precipitation into plain rain. This phase is now expected for Sunday afternoon through early Monday morning.

Phase 3: The Cold Conveyor Belt (CCB). This phase is the least confident and holds the most variability. Once the secondary low is established, wrapped-up and stationary for a few hours off NJ/Delmarva then temperatures will crash as the low slowly pulls away, first aloft and then at the surface. The CCB will no doubt form. The question is will it form in time to dump snow over parts of New Jersey? Or will it form too late and only dump snow over New England? Yesterday the GFS was a go with the Euro a no-go. Today the GFS is a no-go but the Euro just said go. So much volatility as an Upper-Level Low (ULL) is involved in interacting/capturing the secondary surface coastal low. At this point we are just keeping the possibility on the table. If it happens then NNJ and parts of CNJ could be looking at significant snowfall Monday morning through Monday evening. SNJ is not favored for the CCB phase but could end with a little-to-no accumulation snow burst. If it does not happen then precipitation will end on Monday likely in non-wintry form and that will be that. We need another day or two to get a handle on this phase. With the system now being later it bought us some more time to analyze. Otherwise once the system pulls away by Monday night we stay cold into next week with another weekend storm signal to re-evaluate. Let’s get through this system first.

In English: Periods of light rain are possible between now and overnight tonight with generally mild conditions. Temps then drop after midnight as strong winds pick up for Thanksgiving day. Expect gusts to 40mph possible at times out of the NW. It will be a cold and dry Thanksgiving aside from possible non-accumulating flurries (NWNJ most favored). Temperatures should struggle to escape the 40s for high temperatures and wind chills will make it feel even colder especially into Thanksgiving evening/overnight hours.

A snow to ice (sleet/freezing rain) to plain rain situation is then likely NW of the NJ Turnpike this Sunday morning into Sunday afternoon. Areas SE of the NJ Turnpike will likely start as plain rain or quickly changeover. All of NJ then sees plain rain Sunday night into Monday morning which should wash any NWNJ accumulations away. I’m then watching Monday morning through Monday evening for a potential snow dump over NNJ (both NWNJ and NENJ) and possibly parts of NCNJ. SCNJ and SNJ (SW of the NJ Turnpike) would likely end as only rain/flurries. Sunday is fairly confident. Monday has low confidence. I will try to put a video out this evening explaining it in better detail with the freshest data. Have a great rest of your Wednesday and have a wonderful Thanksgiving tomorrow. Be safe! JC

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