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August 2011

Hurricane Irene – Tracking and Chase Potential

Now that we’re getting within a reasonable amount of forecast accuracy, I figured it’s time to make a post about Irene and my chasing prospects.

The models have been consistently trending east with Irene for the past couple of days, but the most recent runs have inched back west as the synoptic setup out west is getting worked out (which will be the kicker that causes Irene to recurve). Observational model biases indicate that the kicker trough will verify more slowly than what is currently modeled, which would allow Irene to work further west. Right now it’s progged to go through (or just east of) the Outer Banks of North Carolina before making landfall on Long Island and the Northeast. Any more of a westward push would send Irene into the Morehead City, NC area or the Delmarva Peninsula, which will be the two areas that Jason (The Weather Warrior) and I will be targeting. Obviously it will have to come down to a decision of choosing just one of these locations, as timing and road closures would make it very difficult, if not impossible to reposition from one area to the other in time.

The decision to go will have to be made tomorrow, as departure time will likely be early Friday. I have discussed the possibility of Irene coming back west, but there is still a good possibility that it could go further east and miss the Mid-Atlantic or even the Northeast, so the next 24 hours of development will be extremely important in zeroing-in on Irene’s track. Right now I’m slightly above 50% GO for chasing.

As it stands, Irene is a Category 3 Hurricane and is expected to intensify a bit more while in/near the Bahamas, with gradual weakening as it nears the East Coast.

Mid-Atlantic Discussion – Aug 21, 2011

It seems like I jinx our severe weather every time I make a post about it. We’ve been faring a lot better with the pulse-type storms than with any sort of organized system this summer, but unfortunately you can’t really chase pulsers since they almost always weaken before you can get to them… not to mention the fact that they almost never produce tornadoes.

Anyway, getting to tomorrow’s threat, we see a cold front and upper-level trough moving through the region, with the best dynamics to our north in PA/NJ/NY up through parts of New England. I’m not particularly thrilled with the setup locally, though it does raise an eyebrow. Most of the concern comes with how the mesoscale features pan out, which the models have had a hard time dealing with since the upper-level energy isn’t that organized. The complicated and convoluted upper-levels, along with weak low-level winds, has been our biggest downfall this summer. Stronger, more highly concentrated features would help improve not only lift but the mid-level lapse rates as well, which is another key to getting well-organized and sustained storms (at least in our region).

Tomorrow looks a bit better than previous setups this summer (mostly due to the better looking lapse rates and possibility of a low-level “jet”) as a cold front and upper-level jet streak move into the region. Lapse rates are good up to 650mb, but the 650mb-300mb lapse rates are fairly poor. A low-level jet could develop tomorrow across the eastern parts of the region, which would help boost storm formation and organization. Another issue is timing, with the storms expected to form before peak heating in most of the region. Pre-frontal rain/clouds are also a concern, thought not so much as they have been in previous setups.

Chase-wise, I would pick eastern PA/NJ or even the Delmarva Peninsula as possible targets unless good storms can get going early in MD/NoVA/central PA. I may have to sit this one out as I am working the overnight tonight, and sleep will weigh into the decision.

SPC’s thoughts:

…NEW ENGLAND/ERN NY/MID-ATLANTIC/CNTRL APPALACHIANS…
A LARGE UPPER-LEVEL TROUGH WILL MOVE EWD ACROSS THE GREAT LAKES AND
OH VALLEY SUNDAY AS A 60 TO 75 KT MID-LEVEL JET ROUNDS THE BASE OF
THE TROUGH. AHEAD OF THE UPPER-LEVEL TROUGH….MODEL FORECASTS
INITIATE NUMEROUS THUNDERSTORMS ALONG AN AXIS OF MODERATE
INSTABILITY FROM WRN NEW ENGLAND SSWWD INTO THE MID-ATLANTIC BY
EARLY SUNDAY AFTERNOON. FORECAST SOUNDINGS ALONG THIS CORRIDOR AT
21Z SHOW MLCAPE VALUES IN THE 1200 TO 2000 J/KG RANGE WITH MODERATE
DEEP LAYER SHEAR AND SOME DIRECTIONAL SHEAR IN THE LOW-LEVELS. AS
THE NOSE OF THE MID-LEVEL JET MOVES INTO THE NERN STATES SUNDAY
AFTERNOON…DEEP LAYER SHEAR WILL INCREASE MAKING CONDITIONS
FAVORABLE FOR SEVERE STORMS ALONG THE INSTABILITY AXIS. IN
ADDITION…MODEL FORECASTS INTENSIFY A LOW-LEVEL JET ACROSS THE
SLIGHT RISK AREA IN THE LATE AFTERNOON SUGGESTING WIND DAMAGE COULD
BE THE GREATEST THREAT. CONSIDERING 500 MB TEMPS SHOULD BE IN THE
-10 C TO -12 C RANGE…HAIL WILL ALSO BE POSSIBLE IN AREAS WHERE
INSTABILITY AND SHEAR ARE MAXIMIZED. ALTHOUGH MORE CONDITIONAL…AN
ISOLATED TORNADO THREAT COULD ALSO DEVELOP NEAR THE CENTER OF THE
LOW-LEVEL JET IN THE MID-ATLANTIC WHERE THE STRONGEST INSTABILITY IS
FORECAST AND SFC DEWPOINTS SHOULD BE IN THE MID TO UPPER 60S F.

Models showing tropical threat to the Southeast late next week

Now that even the Euro Op. is on board with developing a tropical system tracking towards the Southeast coastline, I decided that it’s time to do a write-up about it.

The American models have been fairly consistent with bringing a tropical system into the Southeast, having shown the tropical system for over a dozen consecutive runs. More and more of the European ensemble members, along with the operational, are starting to pick up on it as well. The spread for landfall has been anywhere from Alabama to the Carolinas, but the general timing and region has been fairly consistent. The European models have been more reluctant to develop this system, but the latest run does show better development just off the East Coast. Despite model agreement, this will have to be watched with great scrutiny as it is still a ways out and could change drastically at any time.

The key thing to take away from the models at this range is that the overall pattern is becoming more favorable for a U.S. landfall, regardless of if/when a tropical system develops. The NHC has just labeled this potential system as an invest, so we will have more eyes and models tracking it very soon.

Winter 2011-2012 (DJF) precipitation forecast

The Mid-Atlantic will struggle to get to near normal, but most should be able to edge into that category as the southeastern Mid-Atlantic goes drier than normal again.

As for snowfall, I expect the Mid-Atlantic to be near normal to slightly above normal (90-125%) throughout the region. I think the storm tracks will be similar to last winter, but the winter storms that hit the Southeast and brought anomalously-large snowfall totals to that region will be further north this year due to a weaker trough (and weaker -NAO). That would put the tracks through, or just south of, the Mid-Atlantic. These storms that we didn’t get last year will help boost the region’s snowfall totals, though each individual event may only drop 1-3 inches in most non-mountainous areas.

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This was last year’s DJF forecast and verification:

Mid-Atlantic Discussion – Aug 14, 2011

Clouds and weak LL winds will hurt severe chances today, but okay lapse rates, decent UL support and dewpoints in the lower 70s should help make things a little interesting this afternoon. Secondary low development in NC/S VA certainly won’t help our poor LL wind situation as the SFC winds weaken and become more variable.

RUC shows a much better setup for severe weather in the DC/MD region (which would warrant the slight risk), but it has been overzealous with the wind field and dewpoints in recent events.

SPC was rather bullish this morning… we’ll see what their thoughts are in future updates, as they have been too bullish with the last two systems that have passed through the region.

Winter 2011-2012 (DJF) temperature forecast – First look

Winter 2011-2012:

The monthly breakdown:

METHODOLOGY:

Used rough ENSO analogs (neutral ENSO to weak Nina summer going into weak/moderate Nina), coupled with NAO analogs based on low sun activity leading to -NAO in the winter. I also included -PDO to an extent, put all the factors together and weighted accordingly. Not all analogs fit the NAO/PDO correlations, but still fit most of the requirements.

ANALOGS:
in [year (weight)] format

1995 (more)
2008 (more)
1970 (normal)
2000 (normal)
1962 (less)
2010 (less)

NOTE: Anomalies are against 1971-2000 normals.

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