My last post several weeks ago outlined the 10-15 day thaw for the second half of January, and the potential reload to the pattern for February. Both of those items have verified; we have now entered a regime of renewed high latitude blocking, complete with a severely negative AO, negative NAO, and positive PNA. Tropical forcing has also become significantly more conducive to Eastern US troughiness as I'll detail shortly. The sensible weather results of this pattern have already been experienced for the Mid atlantic states -- a record breaking, historic winter storm, blizzard for some, with widespread 15-25" totals from Washington DC northeastward to Philadelphia and southern NJ. PHL international airport received an unbelievable 28.5", only second to the 1996 blizzard which produced 30.7" there. A few locations in Maryland had totals in the 25-30" range as well.
Moving forward - the clean-up is underway, but all eyes will turn to the medium range threat, which I believe will put the NYC metro area back in the game for meaningful snow. If we take a look at the synoptics for the upcoming event, the 500mb level indicates a short wave with several closed contours surrounding it, barreling eastward across the Plains, Ohio Valley, and finally the northern Mid atlantic, where it will meet upper level confluence to the north, causing the primary wave to transfer its energy to a secondary coastal low near the VA capes. This is when it gets interesting -- warm air advection in association with the energy transfer may yield mixed precipitation as far north as the south Jersey coastline; however, once the coastal storm gains control of the circulation, pcpn will fall as snow in most places. Some modelling indicates the low will intensify rapidly sub 990mb, with strong vertical velocities exploding along the I-95 corridor, particularly from Baltimore northeastward.
Moving forward - the clean-up is underway, but all eyes will turn to the medium range threat, which I believe will put the NYC metro area back in the game for meaningful snow. If we take a look at the synoptics for the upcoming event, the 500mb level indicates a short wave with several closed contours surrounding it, barreling eastward across the Plains, Ohio Valley, and finally the northern Mid atlantic, where it will meet upper level confluence to the north, causing the primary wave to transfer its energy to a secondary coastal low near the VA capes. This is when it gets interesting -- warm air advection in association with the energy transfer may yield mixed precipitation as far north as the south Jersey coastline; however, once the coastal storm gains control of the circulation, pcpn will fall as snow in most places. Some modelling indicates the low will intensify rapidly sub 990mb, with strong vertical velocities exploding along the I-95 corridor, particularly from Baltimore northeastward.
Note on the 00z GFS 500mb depiction valide 18z Wednesday, we see the short wave vorticity sliding southeastward to the VA capes, indicative of that crucial energy transfer mentioned above. This system has the potential to be produce significant (6-11") or even major (12-17") amounts of snow in our region, and yes, totals higher than that cannot be ruled out at this point, Simply an incredible pattern -- all the global indicators are in our favor. The major mid-winter warming of the stratosphere a few weeks ago once again started the ball rolling for a downward propagation of this warmth into the troposphere, forcing a strong -AO and consequently -NAO to develop.
Tropical forcing has been ideal much of this winter with positive OLR anomalies near the dateline in the Pacific, i.e., around ENSO region 3.4 -- a great spot for aiming the cold and snow at the mid atlantic and northeast. Latest GFS ensemble MJO forecasts have it remaining in phase 8 the next couple weeks - again - a conducive phase for low height field downstream on the east coast.
The phase 8 MJO 500mb composite is one that promotes troughiness in the East/below normal temperatures, and blocking across Greenland and the northern latitudes.
Here are my bottom lines to the upcoming pattern:
1) Continued below normal temperature regime through the forseeable future - no sustained warm-ups in sight - the pattern has officially reloaded.
2) Significant to major snow event a legitimate potential for the area; targets this time around should be further north, PHL to BOS corridor rather than RIC, DCA, BWI, although the latter locations can still get sig snows.
3)Long term pattern is one that favors more blocking, more storminess, and more cold. This winter is a tireless engine and will keep trucking on, probably into March.
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