Year: 2015

Cold and Damp Through Thursday…More Warmth and Thunderstorms Friday

Miguel Pierre Severe Wx, Spring Wx

Strong high pressure over SE Canada has cause a strong  cold front to push south into Mid-Atlantic region this evening. We call this a “backdoor cold front”, because it comes from the northeast or east direction instead of the more common northwest or west direction. Behind the fronts, is an ocean-cooled airmass. Temperatures have drop into 40s through the region, as east to northeast winds increase to 15mph to 20mph.  Periods of rain and drizzle have also developed around the region Tomorrow and Thursday will feature periods of rain and drizzle with temperatures in upper 30s to middle 40s through the region. Which 10 to 15 degrees below normal for this time of year.

18zNAMf24

High pressure will begin moving east into the Atlantic on Thursday night and Friday morning. This will cause stronger southerly flow and the front to lift back northward as warm front. Depending on timing and progression of this warm, temperatures could rise back into 60s or 70s in parts of the area. Especially over New Jersey and New York City. A low pressure system tracking into the Great Lakes will push a cold front through area on Friday night. Ahead of this front could some showers and thunderstorms for the Tri-state area late Friday afternoon. The Storm Prediction Center has placed Central and Southern New Jersey in a 15% slight risk for severe thunderstorms on Friday. Where is more likely to be unstable enough for some thunderstorms to reach severe levels.  However, there is some risk for some strong thunderstorms some shear and marginal instability. The main threats are strong winds and heavy rainfall.

day4prob

Behind the cold front, northwest winds will dry us out for a beautiful weekend. Saturday and Sunday will be mostly sunny and with high temperatures in the lower to middle 60s. Except upper 50s near the shores, where sea-breezes will develop late.

Snow Likely for Eastern Long Island and Southeast Connecticut Saturday

Miguel Pierre Winter Wx

No we aren’t done with snow yet. Sometimes winter likes to linger into late March and even April.

An inverted trough with bands of snow will develop over New England and Long Island tomorrow afternoon and evening. This an elongated area of low pressure that extends from a larger storm developing well offshore. Upper-level shortwave energy enhances lifting and instability along this trough. Often there is narrow band of heavier snowfall associated with these troughs. The exact placement and intensity of the banding with these type of systems, are often difficult models to handle and these solutions vary from run to run. At this time it appears, that there is enough agreement to increase chances for accumulating snow tomorrow afternoon and even more so tomorrow night for parts of Long Island and New England.

18zGFSf33The latest run of the 18z GFS, shows a band of moderate to heavy snow falling over Eastern Long Island by tomorrow evening. The GFS sounding over OKX (Brookhaven, NY) shows significant omega values of up to -15 ub/s in snow growth region between 700mb and 800mb. Temperatures early tomorrow afternoon will be middle 30s. So initially some melting will occur, especially the roads and streets. However, after 4pm temperatures will fall into lower 30s and upper 20s as snowfall rates begin to increase and more cold air starts to advect in from the northwest. Snow should start accumulate on most surfaces at this point. At this time, a 1″ – 3″ snowfall looks most likely over Eastern Long Island and Southeast Connecticut. Localized snowfall totals between 3″ to 6″ are possible if heavier banding develops Saturday night. This will continued to be monitored and I will have another update tomorrow morning

18z GFS forecast sounding for Brookhaven, NY at 8pm Saturday
18z GFS forecast sounding for Brookhaven, NY at 8pm Saturday

Elsewhere over tri-state some snow showers or flurries are possible tomorrow afternoon and early tomorrow evening..  These will not amount to much than some dustings or coating on the grass and colder surfaces. These areas will be too far away from the inverted trough. Some places west of New York City may not even see a flake. Snow will begin to end for Eastern Long Island and Southeast Connecticut, after midnight Saturday night. Sunday will become mostly sunny with high temperatures in upper 30s to lower 40s. As high pressure builds in from the west.

Mid-Late March Outlook – Is Winter Over?

Miguel Pierre Long-Range Discussions

After the MJO/tropical weakened during the last week of February, the pacific pattern changed to -PNA pattern. The west ridge retrograded into NE Pacific. However, this also kept the EPO negative and support for a cross-polar flow into US. So the first five days features wintry threats. Including one that gave many parts of the 4″ to 8″ of snow on Thursday, March 5th. We have now finally much warmer temperatures today and for much of this week.Well, enjoy it, because it now looks the MJO will be picking up later this month.. Model forecasts are for the MJO to progress and become very strong into between phases 7 and 8. If we reach phases 8, this support a cooler and stormier pattern to return around or after March 20th:

ALL_emean_phase_full

The +PDO still looks favorable for more -EPO/+PNA pattern to continue to reload into early Spring. The -QBO continues to fall as the  February value was -28.62. This could lead to more planetary waves impacting the the polar vortex. So even if MJO or tropical forcing doesn’t last long, the +PNA (west coast ridge) will likely return and there are some signs of the NAO may go negative for period as well. As we get later in March, climatology favors less snow for the coastal plain. However, the potential for anomalous pattern to show up again, we can’t rule out entirely another moderate or significant snowfall threat for even the coast. Stay tuned

The 12z GEFS showing +PNA pattern around March 20th
The 12z GEFS today  showing +PNA pattern evolving around March 20th