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Winter storm 12/8-9 model discussion part II


Ji

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Re: the comments on the upcoming NAM upgrade...hopefully to go in sometime this spring:

 

North American Mesoscale (NAM) System Use of hybrid-variational-ensemble GSI analysis with global EnKF; modified gravity-wave drag/mountain blocking; new version of BMJ convection with less convective triggering; replace GFDL radiation with RRTM, new version of microphysics (Ferrier-Aligo); explicit convection in all NAM nests except Alaska Spring/Summer 2014
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Seems the consensus is becoming more clear for the front end "finger". Somewhere in the neighborhood of .25 - .30 give or take. Models seem unified in painting the stripe where most of us live. 

 

It's pretty narrow and that will be tough on forecasters. I have a hunch it ends up a bit further north than current runs. 

 

Pretty decent setup for some ice I-95 and east and seems likely that someone to the west will get .25 or maybe more. 

 

Hopefully a drying trend on the first wave doesn't happen. I'm sure most of us would be ok with it as modeled for right now. 

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Re: the comments on the upcoming NAM upgrade...hopefully to go in sometime this spring:

 

North American Mesoscale (NAM) System Use of hybrid-variational-ensemble GSI analysis with global EnKF; modified gravity-wave drag/mountain blocking; new version of BMJ convection with less convective triggering; replace GFDL radiation with RRTM, new version of microphysics (Ferrier-Aligo); explicit convection in all NAM nests except Alaska Spring/Summer 2014

 

 

Thanks for the update.  Appreciate it.

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GGEM showing more front end snow then previous runs...

 

Its also earlier than the GFS and NAM... snow breaks out in N VA by 8 am, which is 3-4 hrs earlier than the GFS/NAM.  GGEM shows about 6 hrs of snow for DCA

 

It also moves to sleet around the same time as the GFS... around 20z

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The NAM can be very useful for specific things...picking up on meso scale features the globals can't but it is not very useful for synoptic scale features.  Ironically the ONLY time I can ever remember it being right against all other guidance was once in 2008, about 36 hours before an event all the globals showed our area getting a nice 3-5" snowfall from a trailing coastal wave, and the NAM was OTS.... For some reason its never right when its showing snow and all the others are not...but the one time everything under the sun has snow and the NAM does not...thats when its right. 

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Its also earlier than the GFS and NAM... snow breaks out in N VA by 8 am, which is 3-4 hrs earlier than the GFS/NAM.  GGEM shows about 6 hrs of snow for DCA

 

It also moves to sleet around the same time as the GFS... around 20z

 

GGEM has the two wave idea.  After the snow from 13z to 19z... mainly sleet with a lil bit of freezing rain till around 10pm. Then there is a lull in precip from around 11pm till 2am (FZDZ?)... then we return to the freezing rain till precip shuts off again around 8am

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This is a crazy storm.  The model variances are pretty cool to watch.  I'm excited about what we might see in the end.

Model variance seems pretty minor overall and has for a few days now.  9.9/10 storms are "tricky" and "very uncertain" here. 

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GGEM has the two wave idea.  After the snow from 13z to 19z... mainly sleet with a lil bit of freezing rain till around 10pm. Then there is a lull in precip from around 11pm till 2am (FZDZ?)... then we return to the freezing rain till precip shuts off again around 8am

 

Pretty dryish. GGEM been leading the way on drier storm. 

 

I_nw_g1_EST_2013120612_063.png

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Model variance seems pretty minor overall and has for a few days now. 9.9/10 storms are "tricky" and "very uncertain" here.

Models have gone back an forth with the dry vs wet for about three days. Yesterday I didn't see this idea of wet, lull, wet. At least not as pronounced as it seems now. They've been pretty steady on the cold, but the timing, extent, and amount of precip seems far from settled to me. If the forecast is for cold with some winter precip on Sunday then yeah, they've been steady.

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The NAM for MRB is UGLY! FWIW. .9 ZR:

 

131208/1600Z 52 09004KT 26.7F SNOW 15:1| 0.4|| 0.00|| 0.00|| 0.025 15:1| 0.4|| 0.00|| 0.00|| 0.03 100| 0| 0
131208/1700Z 53 09003KT 26.7F SNOW 11:1| 0.8|| 0.00|| 0.00|| 0.069 12:1| 1.1|| 0.00|| 0.00|| 0.09 100| 0| 0
131208/1800Z 54 10004KT 26.9F SNOW 4:1| 0.2|| 0.00|| 0.00|| 0.054 9:1| 1.4|| 0.00|| 0.00|| 0.15 100| 0| 0
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131208/1900Z 55 10005KT 27.8F SNOW 7:1| 0.2|| 0.00|| 0.00|| 0.027 9:1| 1.6|| 0.00|| 0.00|| 0.17 100| 0| 0
131208/2000Z 56 11007KT 28.1F SNOW 8:1| 0.2|| 0.00|| 0.00|| 0.022 9:1| 1.7|| 0.00|| 0.00|| 0.20 100| 0| 0
131208/2100Z 57 11006KT 28.1F SNOW 11:1| 0.4|| 0.00|| 0.00|| 0.038 9:1| 2.2|| 0.00|| 0.00|| 0.23 100| 0| 0
131208/2200Z 58 12007KT 27.6F FZRA 0:1| 0.0|| 0.00|| 0.05|| 0.052 9:1| 2.2|| 0.00|| 0.05|| 0.29 0| 0|100
131208/2300Z 59 11008KT 27.6F FZRA 0:1| 0.0|| 0.00|| 0.05|| 0.043 9:1| 2.2|| 0.00|| 0.10|| 0.33 0| 0|100
131209/0000Z 60 12007KT 27.8F FZRA 0:1| 0.0|| 0.00|| 0.03|| 0.032 9:1| 2.2|| 0.00|| 0.13|| 0.36 0| 0|100
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131209/0100Z 61 12007KT 27.9F FZRA 0:1| 0.0|| 0.00|| 0.03|| 0.029 9:1| 2.2|| 0.00|| 0.16|| 0.39 0| 0|100
131209/0200Z 62 12007KT 27.8F FZRA 0:1| 0.0|| 0.00|| 0.01|| 0.006 9:1| 2.2|| 0.00|| 0.17|| 0.40 0| 0|100
131209/0300Z 63 13007KT 28.8F FZRA 0:1| 0.0|| 0.00|| 0.03|| 0.031 9:1| 2.2|| 0.00|| 0.20|| 0.43 0| 0|100
131209/0400Z 64 11004KT 28.3F FZRA 0:1| 0.0|| 0.00|| 0.09|| 0.081 9:1| 2.2|| 0.00|| 0.29|| 0.51 0| 0|100
131209/0500Z 65 12003KT 28.5F FZRA 0:1| 0.0|| 0.00|| 0.06|| 0.057 9:1| 2.2|| 0.00|| 0.35|| 0.57 0| 0|100
131209/0600Z 66 VRB02KT 29.2F FZRA 0:1| 0.0|| 0.00|| 0.06|| 0.058 9:1| 2.2|| 0.00|| 0.41|| 0.62 0| 0|100
----------------------------------------------+----++-----+-------------++--------------++-------------++-----------+---+---
131209/0700Z 67 06003KT 30.1F FZRA 0:1| 0.0|| 0.00|| 0.23|| 0.220 9:1| 2.2|| 0.00|| 0.64|| 0.84 0| 0|100
131209/0800Z 68 11003KT 30.5F FZRA 0:1| 0.0|| 0.00|| 0.06|| 0.061 9:1| 2.2|| 0.00|| 0.70|| 0.91 0| 0|100
131209/0900Z 69 10004KT 31.0F FZRA 0:1| 0.0|| 0.00|| 0.06|| 0.053 9:1| 2.2|| 0.00|| 0.76|| 0.96 0| 0|100
131209/1000Z 70 13005KT 31.9F FZRA 0:1| 0.0|| 0.00|| 0.14|| 0.134 9:1| 2.2|| 0.00|| 0.90|| 1.09 0| 0|100

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WASHINGTON-EXTREME WESTERN ALLEGANY-CENTRAL AND EASTERN ALLEGANY-
AUGUSTA-ROCKINGHAM-SHENANDOAH-FREDERICK VA-PAGE-WARREN-CLARKE-
NELSON-ALBEMARLE-GREENE-WESTERN HIGHLAND-EASTERN HIGHLAND-
HAMPSHIRE-MORGAN-BERKELEY-JEFFERSON-HARDY-WESTERN GRANT-
EASTERN GRANT-WESTERN MINERAL-EASTERN MINERAL-WESTERN PENDLETON-
EASTERN PENDLETON-
INCLUDING THE CITIES OF...HAGERSTOWN...FROSTBURG...CUMBERLAND...
STAUNTON...WAYNESBORO...HARRISONBURG...WINCHESTER...FRONT ROYAL...
CHARLOTTESVILLE...HIGHTOWN...MONTEREY...MARTINSBURG...
CHARLES TOWN...MOOREFIELD...BAYARD...MOUNT STORM...PETERSBURG...
ELK GARDEN...KEYSER...FORT ASHBY...CIRCLEVILLE...FRANKLIN
1207 PM EST FRI DEC 6 2013

...WINTER STORM WATCH IN EFFECT FROM SUNDAY MORNING THROUGH
MONDAY MORNING...

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS
ISSUED A WINTER STORM WATCH...WHICH IS IN EFFECT FROM SUNDAY
MORNING THROUGH MONDAY MORNING.

* PRECIPITATION TYPE...SNOW AND SLEET WILL CHANGE OVER TO ALL
FREEZING RAIN SUNDAY AFTERNOON AND LASTING THROUGH MONDAY
MORNING BEFORE CHANGING TO RAIN MONDAY AFTERNOON.

* ACCUMULATIONS...2 TO 4 INCHES OF SNOW AND SLEET AND A QUARTER
INCH OR MORE OF ICE ACCUMULATION. ACCUMULATIONS UP TO A HALF
INCH POSSIBLE AT ELEVATIONS BELOW 1500 FEET.

* TIMING...SNOW AND SLEET ARE EXPECTED TO BEGIN IN THE CENTRAL
FOOTHILLS AND SHENANDOAH VALLEY SUNDAY MORNING AND SPREAD
NORTHWARD ACROSS NORTHERN VIRGINIA...THE EASTERN PANHANDLE OF
WEST VIRGINIA AND THE POTOMAC HIGHLANDS BY LATE SUNDAY MORNING.
A CHANGEOVER TO FREEZING RAIN IS EXPECTED MIDDAY SUNDAY AND
CONTINUING INTO THE NIGHT BEFORE CHANGING OVER TO RAIN MONDAY
MORNING. ELEVATIONS ABOVE 1500 FEET WILL CHANGEOVER TO ALL RAIN
SUNDAY EVENING.

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