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May 2011 NYC metro area obs./discussion


tmagan

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this upper level low's rainfall is starting to look more convective than synoptic...and if that's the case, we would be spared any overly significant rain totals. we shall see..

I am really suspicious of the HPC QPF map...it seems high to me. I think the bulk of the heavy synoptic rainfall is going to occur just north of the frontal boundary well to our north, in Upstate NY, extreme NNE, and parts of Quebec. These are the areas that could see 4"+ of rainfall.

For the NYC metro, I expect sporadic showers/thunderstorms; it's just difficult to achieve massive widespread QPF totals with a surface low tracking to the west of the region. Warm sector precipitation tends not to be uniform enough to produce the QPF advertised by the HPC, and to some degree the 12z ECM. I do think we'll see some heavier stratiform rainfall as the ULL moves off to the northeast, probably on Thursday. But there should be a break on Wednesday, and only occasional showers tomorrow and Monday.

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I am really suspicious of the HPC QPF map...it seems high to me. I think the bulk of the heavy synoptic rainfall is going to occur just north of the frontal boundary well to our north, in Upstate NY, extreme NNE, and parts of Quebec. These are the areas that could see 4"+ of rainfall.

For the NYC metro, I expect sporadic showers/thunderstorms; it's just difficult to achieve massive widespread QPF totals with a surface low tracking to the west of the region. Warm sector precipitation tends not to be uniform enough to produce the QPF advertised by the HPC, and to some degree the 12z ECM. I do think we'll see some heavier stratiform rainfall as the ULL moves off to the northeast, probably on Thursday. But there should be a break on Wednesday, and only occasional showers tomorrow and Monday.

Could not agree more. Tomorrow is kind of interesting, if some of the models are correct and the dry slot can allow for some clearing into NJ, there could be some stronger thunderstorms. We shall see.

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Could not agree more. Tomorrow is kind of interesting, if some of the models are correct and the dry slot can allow for some clearing into NJ, there could be some stronger thunderstorms. We shall see.

I'm glad to hear someone shares my input...I've been mentioning this idea in the SNE forum, but they seem to side more towards the heavier totals shown by HPC and the ECM, rather than the GFS and our thinking. That could also be because a lot of SNE's terrain, especially the ORH hills, has an upslope component on E/SE winds which we'll see during this storm. That may add to rainfall totals for stations like MQE and ORH, as well as for places on the eastern side of the Catskills and Poconos like the Catskill Escapment, where rainfall could be enhanced orographically. The fact that this is a long-duration storm means that elevated areas may see more than the advertised QPF, with those frames of .01" or .1" really adding up for places with enhancement on an E/SE flow.

0z GFS doesn't show too much potential for clear skies tomorrow with around .1" QPF for each frame for NYC metro, except on eastern LI where the marine layer should inhibit any serious thunderstorms. Upton has added thunderstorms to the forecast, so we'll see. We've got a juicy synoptic trigger but surface-based instability may be limited in many areas.

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.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...

INCREASING THETA-E SUN. H2 JET ACROSS ERN CANADA WILL ALLOW FOR

FAVORABLE UPPER LEVEL DIVERGENCE IN THE RR QUAD OVER THE CWA. KI

INCREASES TO AROUND 33. FCST THEREFORE IS FOR SHRA AND TSTMS.

LOCALLY HEAVY RAIN POSSIBLE. SFC BASED INSTABILITY RELEGATED TO

THE NJ ZONES AND PORTIONS OF THE LWR HUDSON VALLEY. ALTHOUGH CAPE

GENERALLY AOB 400 J/KG...THERE WILL BE A WINDOW IN THE LATE

AFTN...ESPECIALLY IN NJ...WHERE MID LEVEL DRY SLOT MAY ALLOW FOR

PARTIAL CLEARING AND A BOOST IN SFC TEMPS. IF THIS HAPPENS...AN

ISOLD STRONG CELL IS POSSIBLE IF THE WARMING ALOFT DOESN/T CAP

THINGS.

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I'm glad to hear someone shares my input...I've been mentioning this idea in the SNE forum, but they seem to side more towards the heavier totals shown by HPC and the ECM, rather than the GFS and our thinking. That could also be because a lot of SNE's terrain, especially the ORH hills, has an upslope component on E/SE winds which we'll see during this storm. That may add to rainfall totals for stations like MQE and ORH, as well as for places on the eastern side of the Catskills and Poconos like the Catskill Escapment, where rainfall could be enhanced orographically. The fact that this is a long-duration storm means that elevated areas may see more than the advertised QPF, with those frames of .01" or .1" really adding up for places with enhancement on an E/SE flow.

0z GFS doesn't show too much potential for clear skies tomorrow with around .1" QPF for each frame for NYC metro, except on eastern LI where the marine layer should inhibit any serious thunderstorms. Upton has added thunderstorms to the forecast, so we'll see. We've got a juicy synoptic trigger but surface-based instability may be limited in many areas.

probably has something to do with their latitude too...they are much further north and closer to the front and better synoptic support for heavy rain.

speaking of the convection, i just posted uptons discussion where they talk about the clearing and potential instability/storms.

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probably has something to do with their latitude too...they are much further north and closer to the front and better synoptic support for heavy rain.

speaking of the convection, i just posted uptons discussion where they talk about the clearing and potential instability/storms.

I just wonder if we'll get into this situation where we're stuck between the two sources of rain: heavy synoptic forcing to the north along the frontal boundary, and heavy convection to the south where there's more clearing and higher temperatures (WRF seems to be playing into this). It also depends greatly on the position of the warm front, which has been a point of disagreement between the GFS and NAM. The 0z NAM at 42 hours has the 10C 850mb contour running directly though NYC metro, whereas the 0z GFS at the same time has the 10C contour almost 100 miles to the NW of the City. The difference in the positioning of the warm front was even more remarkable on the 18z runs, especially over New England where the NAM had 10C 850s up to the Mass Pike whereas the GFS lifted them into North-Central VT/NH.

Where the front sets up Monday could be the focal point for bouts of +RA, although it's almost assuredly going to be north of us.

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coastal flooding middle of the week? Onshore flow starts today and we have a full moon on wed

The flow probably isn't going to be strong enough.

There will be flooding but it wont be coming from the ocean lol.

dont underestimate persistant SE flow and a lunar high tide. I think at least minor coastal flooding is likley by tuesday / wed.

Upton,

.TIDES/COASTAL FLOODING...

MINOR COASTAL FLOODING LOOKS LIKELY FOR THE NIGHT TIME HIGH TIDE

CYCLES FOR THE NEXT SEVERAL DAYS. IN FACT...MODERATE BENCHMARKS

COULD BE REACHED BY MID WEEK AS BOTH EASTERLY WINDS AND ASTRONOMICAL

TIDES HEIGHTS INCREASE AS FULL MOON APPROACHES.

IN THE MEANTIME...SWELLS FROM A PERSISTENT SE WIND...AND HIGH

ASTRONOMICAL TIDES WILL RESULT IN MINOR COASTAL FLOODING TONIGHT.

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The models from yesterday missed the heavier rains that fell in spots around the

area this morning.

This SREF forecast just runs through 0z Thursday and some of the members have

4+ inch maxes in spots that pick up the heaviest rains through then.It's not unusual

for the models to underestimate rainfall totals associated with cutoff lows especially

in the localities that see the heaviest totals.

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