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RIC Airport

Richmond Metro/Hampton Roads Discussion

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Spring can go ahead and arrive now. I don't see us getting anymore snow the way this pattern is. Technically, RIC did get above average snowfall but almost all of it came back on the December event. Since then it's been cold rain. 

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Can't say I call it just yet the Next Weds- Monday time frame will be our best hope in awhile.. Nothing certain but Def still a chance.. ha

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12 hours ago, eaglesin2011 said:

Can't say I call it just yet the Next Weds- Monday time frame will be our best hope in awhile.. Nothing certain but Def still a chance.. ha

I'm calling it. We are done. Persistence this winter has been north and west. 12/9 was a fluke. On to 2019-20. 

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12 minutes ago, RIC Airport said:

I'm calling it. We are done. Persistence this winter has been north and west. 12/9 was a fluke. On to 2019-20. 

I’m calling it too even up here.  This event is the shovel of dirt in my 6ft hole.  19-20 will be rockin’

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3 minutes ago, wasnow215 said:

Any thoughts on tomorrow night’s/overnight into Monday severe threat?

LWX had a great write up in their evening AFD that I posted in the catchall severe thread... dunno what Wakefield is saying though

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April 17, 2019

this Wednesday afternoon

502 PM EDT

 * * * *  Severe Weather & Heavy Rainfall event for Eastern Virginia  * * * * 

 * * * *  Coming for Friday afternoon & Friday night, 4/19/2019  * * * *

 * * * *  Tornado Watches, warnings, & urban-small stream flood advisories likely * * * *

I.  Introduction.

So the way I see this upcoming Friday afternoon, 4/19, & night event playing out is this:  I see 2 rounds of inclement weather moving in to the Richmond, VA & Eastern Virginia region starting-up early Friday afternoon.  This 1st phase on Friday afternoon, I think will bring the attendant severe weather risk of a wind damage threat & some tornadoes, too.

The 2nd phase of this event I believe will evolve on Friday night, & take shape as a heavy rainfall event, through the late night hours.

II.  Friday afternoon Severe Weather.

I'm going to quantify the severe weather threat in a numbers sense, by touching on the calculated indices.

Here's a look at the severe weather parameters, advertised on Friday afternoon, CENTERED on Richmond, VA, at 2 PM Friday:

#1.)  SB-Cape:  2 PM-5 PM Friday -- Averaging about 1,000 J/kg, varying 750 J/kg from Gfs; 1250 J/kg Nam  This average amount of 1,000 J/kg will be sufficient to sustain convective severe storms on Friday afternoon, with no doubts.

#2.)  SWEAT index -- 2 PM Friday:  321 - 349.  This assesses the tornado risk.  I pay close attention when this value reaches 350+.   To get large tornadoes a high degree of instability with high wind shear gets involved.  I also watch for a BACKED surface wind, and arched hodographs.  Straight-lined hodographs are indicative of a squall line, or line echo wave patterns, lewps.  I don't see much directional shear here, with winds coming from a Southerly direction through the depth of the troposphere.  This value upwards to 349 is marginally close enough to continue the watch for a few or several tornado warnings, owing to the cape & shear values present.

#3.)  TT's:  of 46-48 for Friday afternoon.  This is a non-player for Friday afternoon & night, as this parameter is focused on assessing the hail threat, with its examination of the thermal profile comparisons aloft at different layers.  Values at and above 50 indicate severe storms, and in the mid 50's, scattered severe storms.  But values now are shown to be mid to upper 40's.  

#4.)  Calculated PEAK WIND GUSTS:  52 kts, Gfs; 54 kts, Nam between 11 AM to 5 PM Friday 52 kts = 60 mph; 54 kts = 62 mph.

The 54-hr Nam forecast Skew-T sounding shows the presence of an inverted-V sounding at 2 PM Friday.  This along with the NOSE of an approaching jet max at 850 mb, 5K ft, level at speeds of 40 kts increase to 55 kts, will be sufficient to produce and enhance microbursts & downdrafts.  The leading edge of an accelerating jet max in the lower levels as this has well been known to de-stabilize the atmosphere by instigating the formation of warm-air advective showers & thunderstorms, at the gradient of the change, as it punches Northbound.  This will be in play on Friday afternoon over Eastern Virginia.  Watch for attendant severe weather in the form of wind damage by fast-racing showers & storms.

#5.)  0-6 km shear, (deep shear) -- Values appearing between 47 kts, Nam to 56 kts, Gfs for Friday afternoon in Richmond, VA.  Minimum threshold desired for severe weather is 40 kts; this is already forecast to be exceeded.  

#6.)  500 mb, ~18K-19K ft winds:  Forecast at 55 kts to 70 kts between 2 PM and 8 PM Friday afternoon.  I look for a minimum value of 40 kts to be reached for severe weather, so this amount forecasted well exceeds this for the promulgation of severe storms, at the mid-level altitudes.   At 250 mb, in the highest altitudes, ~35K ft, only 60 kts is forecast.  While not a particularly necessary condition, it's great when winds at this level exceed 100 kts, as a dynamic suction vacuum aloft, as it helps increase UVV's, as what transpired in your late Sunday night even.  But more importantly, the lower levels are where high winds are needed to produce the damaging wind gusts, which will be present at 850 mb.

#7.)  PW, preciptable water, moisture values escalate quickly between Friday morning to Friday afternoon, between 0.97" 8 AM Friday to 1.68" Friday at 2 PM, Nam; and 1.2" 8 AM Friday to 1.7" 2 PM Friday by Gfs.  All the right ingredients at all the right timing together should quickly inflate this event to severe levels on Friday.  Sudden increase in moisture; sudden increase in low & mid-level jets, sudden increase in SB-cape, and rising of instability with daytime heating, although will be preceded by cloud cover.  

III.  Heavy Rainfall Event, Friday night.

Whenever I spot this pattern of a closed upper 500 mb low, slowly approaching with a LENGTHY, fetch of meridional 500 mb flow from South-Southwest at all levels of the troposphere, at terrific speeds of 40-60 kts from boundary layer to mid-levels, then this *screams* th words heavy convective rainfall all over it, for Friday night.  Having been a long-time resident of New Orleans for 17 years of my life, I've come to recognize these pattern settings down South.

Of particuarly importance that I've also spotted is your 12Z Gfs rainfall grid that depicts what I call a RATHER SLOW progression of a thick, heavy rain band which only moves from Western Virginia at 2 PM Friday over to Eastern Virginia 12 hours later, at 2 AM Saturday.  Gang, that's a SLOW 12-hour progression, only going from Western Virginia to Eastern Virginia in a 12-hour span of time.  And this is coming from a model who's notoriously biased in being overly progressive in moving out rain quickly.  

Additionally, I see a sharp uprising in PW's from 1.20" 8 AM Friday up quickly to 1.70" 6 hours later, at 2 PM Friday afternoon, coincident with the nose of an 850 mb low-level jet increasing during peak heating time & instability time as well.

Whenever I see 3-hour rain rates of 3/4" to 1" being advertised 54-60 hours in advance over a progressive 12 hour period across the state of Virginia in the coarser grid domain of the GFS, I can only be thinking that once this hits the finer-mesh resolution grids of H-Rap & WRF, that these rainfall rates will be AMPLIFIED SO MUCH GREATER.  PLUS, I also have to be thinking there will be numerous heavy bands of 50+ dbz rates.  And when that happens amidst a strengthening powerful low-level & mid-level jet structures in the presence of modest, but ample levels of SB-Cape, then this spells both a severe risk & heavy rainfall potential that looks pretty certain to unfold on Friday afternoon & Friday night.  I think 1" to 3" of rainfall will be commonplace for rainfall totals between Friday afternoon & Friday night.  

Any stalling of this heavy rain banding that sets up meridionally, from South to North will accentuate rainfall totals beyond 4" for any temporal stalling of this heavy rainfall in areas as it slowly crawls Eastbound.

Last Sunday night's event escaped everyone's attention because of the inopportune timing of 1 AM and 4 AM, while nearly most were sleeping.  Not this time.  This time many of you will be up to watch it on radar & feel the experience for yourselves.  

 

--  cyclogenesis 

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April 19, 2019

this Pre-Dawn Friday morning

115 AM EDT

 

* * *  Still a good chance for severe storms & HEAVY RAINFALL for the Richmond, VA area, Friday afternoon & Friday night, 4/19  * * *

* * *  Tornado watches likely to be issued by early Friday afternoon, for Richmond & Eastern Virginia * * *

* * *  Predominant threat still looks to be spots of wind damage & heavy rainfall, ponding of water * * * 

* * *  3 distinct rounds of storms coming  * * * 

 

I.  Timing for Richmond, VA.

 

I'm seeing 3 distinct time periods for showers & storms for Richmond, VA on Friday.  The first wave comes betweeen 3 PM and 4 PM.  The 2nd more serious severe round of weather comes in the evening hours between 5 PM and 7 PM, and then after 8 PM, comes the 3rd round which I think will be the heavy rain period spanning from 7 PM onward to 11 PM.

Viewing late this Saturday night, at timing progressions, appears this weather event will present itself starting as soon as early Friday afternoon, in the form of detached showers randomly racing Northward through the area.  Shower activity will first start out WEST of us and SOUTHWEST of us in the late morning hours.  Then, about the timing in the early afternoon, between 12 PM and 2 PM, I think the 1st tornado watch will be issued close for Richmond.  Storm warnings for detached multi-cellular activity should come between 1 PM and 5 PM.  Interestingly enough, WRF's animation shows NO pockets or LINES of 40+ or 50+ 10 meter surface wind gusts in its 1-hour grids, as I step through its 00Z, 4/19 output.  Non-important, low-ranking moisture advection showers will begin racing Northbound late Friday morning in our area, with SB-Cape increasing during the 11 AM to 2 PM time frame. 

II.  More details. 

Discrete & unattached multi-cellular showers & a few storms should develop across the area between 11 AM and 2 PM, well ahead of the parent line, since a strong morning capping inversion at 8 AM, shown at 12Z/8AM on Nam's 12 hr depiction btwn 800 mb - 750 mb withers away completely by 2 PM, with 0 CINH, (convective inhibition) remaining by 2 PM.   

It's appearing there'll be a revised 750 J/kg, to at most 1,000 J/kg of SB-Cape available for Friday afternoon's storms in the Richmond area. 

While severe weather parameters such as SWEAT, Cape, helicity, Total-totals have all de-escalated since I last wrote you, and numbers have come down a bit, it cannot be ignored that a stout 45kt-55 kt low-level 850 mb jet and 55-60 kt 500 mb jet will be overhead during peak afternoon hours, concurrent with rising Cape levels, although still a bit on the low side of 750 - 1000 J/kg.  While neither speed shear nor directional shear for long-lived supercellular storms are present, the overall wind momentum throughout the depth from boundary layer to mid-levels is impressive enough to be able to transport some of this high wind momentum downward in the heaviest rain shafts produced of the multi-cellular & linear squall line modes.  You generally see a greater occurrence of wind damage with a veered WESTERLY component, but in this case we're dealing with a SOUTHERLY direction, and a fetch of deeper moisture, which is why I believe the heavy rain & flooding threat is kept alive for Friday night across Virginia.  So, not the most idyllic directional consideration for production of severe winds, the speeds are still great enough to produce instances of wind damage.

Also, on account of the TIMING of day, during the afternoon hours, helicity is shown to run upwards to 300 m2/s2 by WRF's modeling scenario, while NAM shows a spiked pocket of 350 to 500 m2/s2 helicity at 5 PM very near the Richmond area.  WRF's maximized CAPE timing is shown to come about 6 PM to the RVA area, right along the SAME TIMING of an approaching squall line to Richmond in the LATE afternoon hours between 5 PM and 7 PM.  

This timing of late afternoon & early evening 5 PM to 7 PM looks to correlate to the highest amount of Cape nearest to Richmond, at a timing when a squall line should be traversing the scene, along with the helicity, so tornado threat & SEVERE WIND THREAT look to be MAXIMIZED, I believe, at this timing of late afternoon & early evening for Richmond. 

Beyond 7 PM, it's a matter of how much RAIN & STORMS LINGER stagnate behind the parent line, as this is where I see the heavy rainfall event unfolding from Friday evening in to Friday night, from 7 PM to 11 PM.  This is the timing for a few flood warnings to be issued.  A higher BAND of PW's, precipitable waters, (1.6" to 1.85"), arrives our area between 11 AM to 2 PM, and REMAINS this HIGH, onward to 11 PM, Friday night.  Virginia Beach & the Hamptons looks to get their heaviest rain threat later in the night, 11 PM to 2 AM.  All of this mess scoots out the area by sunrise, Saturday.

 

-- cyclogenesis    

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