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Abstract: As we ascend into the ensuing warm season, positive ENSO conditions will remain, although with a rather abstemious oceanic profile, indicative of only warm neutral to potentially weak El Nino status. Atmospheric angular momentum has been positive, redolent of Nino-esque conditions, but there has been a negative diminution in FT/MT in recent weeks, which, when analyzed adjunctively with the rapidly cooling sub-surface profile, may be suggestive of a gradually decaying El Nino in the longer term. Positive QBO status, solar minimum, near neutral PDO, and slightly positive AMO are some of the disparate varies under considerations. The highly heterogenous permutation of factors leads to 2002 and 2006 as the most preeminent, similar years in the dataset. The late spring final warming in the stratosphere aided – in concert with subtropical momentum transport – in producing a blocky northern hemisphere for the month of May. However, the down-well effects will not be interminable; they will disintegrate in ensuing weeks. While high latitude blocking may spasmodically develop during the summer, the profile should be characterized by westerly momentum predominance in the mid-latter part of the summer. Consequently, the sensible weather impacts include higher than normal geopotential heights across most of the United States. This will be a hotter than normal summer for most interests near the West and East Coasts. There is potential for period(s) of extreme heat. Protracted, tropical dew points akin to 2018 are unlikely; however, a generally hot and humid summer is on the way for much of the country, with plentiful rainfall from the Mid-west to Northeast.

Key Points:
1) Subsurface ocean temperatures have been cooling significantly across the tropical Pacific in recent weeks, likely redolent of a potentially, slowly decaying El Nino. However, surface warmth will probably remain sufficient to maintain warm neutral to weak El Nino oceanic conditions for the ensuing summer.


2) Sea surface temperature anomalies are reflective of a near neutral PDO and slightly positive AMO. The structure of the SSTA profile is congruous with 2002. Note below: comparison between May 2019 and May 2002; there is a similar orientation of warmth in the central/west Pacific, cooler near California; and, in the Atlantic Ocean, an ostensible cold pool southeast of Newfoundland, bounded by warmth to the south [elongated from the Gulf of Mexico toward Bermuda] and to the north near Greenland. 2006 is also somewhat similar, although less so than 2002.




3) Atmospheric angular momentum propensity has been elevated in recent months; as further indicated by low magnitude GWO orbits through the Nino-esque octants 5-8. However, recent weeks have seen increasingly negative frictional torque, negative EA MT, which will be reflected in an AAM decline, to a certain extent. Additionally, the zonal wind profile across the tropical Pacific looks quite, “mediocre,” meaning, an atmosphere generally devoid of robust westerly wind bursts. I anticipate a heterogeneous summer complete with countervailing easterly trade winds and the spasmodic CCKW/MJO induced westerly wind burst. As seen in 2002 and 2006, these summers featured a mercurial summer of modest +AAM and -AAM momentum transport poleward through the northern hemisphere; a largely unremarkable snapshot from a momentum perspective. In 2006, the predilection for more easterly momentum in the higher latitudes in May reversed for most of the ensuing summer, leading to predominately neutral to positive NAO conditions.


4) The velocity potential / chi z200 profile has ineluctably resembled a weak El Nino in recent months and will probably continue to maintain a modest walker cell circulation with low-frequency uplift in the eastern Pacific. I expected similar tropical forcing to the summer of 2002, as depicted below.


5) Like 2002 and 2006, this will be a weak El Nino summer in concert with a stratospheric backdrop of moderate to strong +QBO conditions. This permutation typically yields less protracted, anomalous high latitude blocking, with AO/NAO conditions averaging near neutral or potentially positive. The recent, robust down-well of the dynamically coupled strat-trop energy transfer should begin to wane deeper in the month of June. Consequently, I expect that June may be most affected be vestigial stronger high latitude blocking. Additionally, easterly momentum remains in the high latitudes from a prior sub-tropical momentum burst. This, too, will gradually reverse in about 3-5 weeks.
6) Global temperatures have been running warmer than normal [top 10 warmest] in recent months. The availability of airmasses sufficient to produce protracted cooler than normal conditions in the NHEM is presently, fairly diminutive.
7) Solar conditions are more harmonious with 2006 than 2002; namely, a solar minimum in the former. Concordantly, cosmic ray induced heightened condensation is higher, and likely has contributed to enhanced rainfall across parts of the United States, in accordance with Smin. The PDO is also more positive this year, versus 2002 or 2006, which should promote [in conjunction w/ the tropical forcing] more geopotential height rises near the West Coast and a more active jet dipping equatorward over the Mid-west/Lakes.
8) Seasonal model guidance: generally in concordance with the notion that early summer features the greatest proclivity for troughing in the Lakes/Northeast due to high latitude blocking, followed by lessening blocking as the summer progresses, overall.
9) Top analog years, based upon an amalgamation of variables such as ENSO, QBO, PDO, AMO, solar, and AAM/GWO are 2002 and 2006.
The following is the June-August analog result for temperature anomalies, and subsequently, precipitation anomalies.




Summer Progression
This will be a hot summer in the East and Northeast relative to normal, with the hottest temperatures relative to normal attained in either July or August. The coolest of the three meteorological summer months relative to normal should be June; while July, or more likely, August, features the highest temperature departures. Residual high latitude blocking may persist for much of June, permitting more frequent trough amplification events in the northern tier of the United States. By July, the Western Ridge may frequently connect with the Atlantic ridge, leading to intervals of very hot, zonal flow. Peripheral convection is likely across the northern tier from the Mid-West to New England. 2002’s hottest month was August, while 2006’s was July [relative to normal]. However, regardless, I expect both July and August to be hotter than normal. There is no strong signal for one month being more wet than another relative to normal. Nonetheless, an active convection summer is anticipated for the Northeast. One or more high-end heat waves may impact the region in either (or both) July and August.
Temperature Departures for June-July-August (JJA) mean, NYC-NJ metro area: +1 to +2
[Favored progression: +1 June, +2 July, +2 August; indicative of a modestly hotter than normal summer]
Precipitation Departures: Above/wetter than normal

90 Degree Day Projections:
BOS: 14
NYC: 26
LGA: 30
EWR: 33
PHL: 36
DCA: 45
RDU: 52



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