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March 5th Snow Threat


WxUSAF

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Ah yes, but that CAA is rooted in the sub-750 mb layers. Given the SE ridge and +NAO, the SW flow above 850 mb should continue during the majority of the event, which is gonna keep temps at that level marginal. When the 800-750 mb flow switches more W-NW, while the CAA may finally be working in, it's also likely syranora to the deep (sufficiently deep) moisture.

Would be funny if this turned into a sleet storm down here!

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BWI sounding at 6Z Thursday morning.....that would be snow with some rimming with the ripping that would be occurring

an hour later, it's fatties

LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg-------------------------------------------------------------------------------SFC 1007    79  -0.2  -0.9  95  0.7  -0.5   0  13 272.4 272.9 272.3 282.0  3.56  1 1000   139  -0.7  -1.1  97  0.4  -0.9   1  18 272.5 273.1 272.3 282.0  3.52  2  950   546  -3.5  -3.6  99  0.1  -3.6 356  28 273.6 274.1 272.3 282.0  3.08  3  900   974  -3.1  -3.3  98  0.2  -3.1 324  29 278.3 278.9 275.4 287.6  3.33  4  850  1429  -0.6  -0.8  99  0.2  -0.7 279  25 285.5 286.2 280.2 297.5  4.24  5  800  1915   0.3   0.1  99  0.2   0.2 247  30 291.5 292.3 283.6 305.4  4.82  6  750  2432  -0.2  -0.5  98  0.3  -0.3 241  41 296.4 297.2 285.7 310.9  4.94  7  700  2984  -1.6  -1.7  99  0.1  -1.6 239  51 300.8 301.6 287.2 315.3  4.82  8  650  3573  -3.3  -3.5  99  0.1  -3.4 235  62 305.2 306.0 288.5 319.2  4.56  9  600  4204  -6.1  -6.2  99  0.1  -6.1 234  69 309.1 309.8 289.3 321.7  4.02 10  550  4881  -9.5  -9.6 100  0.1  -9.6 235  74 312.8 313.4 289.8 323.5  3.36 11  500  5612 -13.7 -13.7  99  0.1 -13.7 239  78 316.4 316.9 290.3 325.0  2.64
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6Z Thursday at DCA

LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg-------------------------------------------------------------------------------SFC 1010    58   0.4  -0.2  96  0.6   0.2   8  11 272.8 273.4 272.8 282.9  3.74  1 1000   137  -0.1  -0.6  96  0.5  -0.3   8  16 273.1 273.7 272.9 283.0  3.66  2  950   546  -2.9  -3.0  99  0.1  -3.0   1  25 274.2 274.7 272.9 283.0  3.21  3  900   974  -2.3  -2.5  98  0.2  -2.4 324  27 279.1 279.7 276.1 288.9  3.52  4  850  1430   0.0  -0.1  99  0.1  -0.0 270  18 286.2 286.9 280.8 298.8  4.46  5  800  1918   1.0   0.7  98  0.3   0.8 241  27 292.2 293.1 284.1 306.7  5.03  6  750  2437   0.6   0.0  96  0.6   0.3 239  39 297.2 298.1 286.1 312.3  5.10  7  700  2990  -1.2  -1.3  99  0.2  -1.3 235  49 301.2 302.1 287.5 316.1  4.95  8  650  3579  -3.1  -3.3  99  0.2  -3.2 229  61 305.4 306.3 288.6 319.6  4.61  9  600  4211  -5.8  -5.9  99  0.1  -5.8 230  71 309.5 310.2 289.5 322.3  4.11 10  550  4889  -9.1  -9.2  99  0.1  -9.1 236  77 313.3 314.0 290.1 324.4  3.47 11  500  5621 -13.3 -13.4  99  0.1 -13.3 244  82 316.9 317.4 290.5 325.8  2.73
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Would be funny if this turned into a sleet storm down here!

...which is my fear. From a "conceptual model" standpoint, the synoptic setup and profiles are screaming sleet (or at least more than just your transient period of sleet) as much as the setup was screaming ice storm Sunday.

PDII back in Feb '03 game me about 3-4" of sleet down in the RIC area. I'll pass, thank you!

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6Z Thursday at DCA

LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg-------------------------------------------------------------------------------SFC 1010    58   0.4  -0.2  96  0.6   0.2   8  11 272.8 273.4 272.8 282.9  3.74  1 1000   137  -0.1  -0.6  96  0.5  -0.3   8  16 273.1 273.7 272.9 283.0  3.66  2  950   546  -2.9  -3.0  99  0.1  -3.0   1  25 274.2 274.7 272.9 283.0  3.21  3  900   974  -2.3  -2.5  98  0.2  -2.4 324  27 279.1 279.7 276.1 288.9  3.52  4  850  1430   0.0  -0.1  99  0.1  -0.0 270  18 286.2 286.9 280.8 298.8  4.46  5  800  1918   1.0   0.7  98  0.3   0.8 241  27 292.2 293.1 284.1 306.7  5.03  6  750  2437   0.6   0.0  96  0.6   0.3 239  39 297.2 298.1 286.1 312.3  5.10  7  700  2990  -1.2  -1.3  99  0.2  -1.3 235  49 301.2 302.1 287.5 316.1  4.95  8  650  3579  -3.1  -3.3  99  0.2  -3.2 229  61 305.4 306.3 288.6 319.6  4.61  9  600  4211  -5.8  -5.9  99  0.1  -5.8 230  71 309.5 310.2 289.5 322.3  4.11 10  550  4889  -9.1  -9.2  99  0.1  -9.1 236  77 313.3 314.0 290.1 324.4  3.47 11  500  5621 -13.3 -13.4  99  0.1 -13.3 244  82 316.9 317.4 290.5 325.8  2.73

Profile is quite a bit better at DCA, but right along that tight boundary it will be ripping ass. 

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DCA at 9Z Thursday

LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg-------------------------------------------------------------------------------SFC 1011    58  -1.6  -2.1  97  0.4  -1.8  10  13 270.7 271.2 270.8 279.4  3.24  1 1000   142  -2.2  -2.7  97  0.5  -2.4  10  18 270.9 271.4 270.7 279.4  3.13  2  950   548  -5.3  -5.3 100  0.0  -5.3  10  24 271.8 272.3 270.7 279.2  2.70  3  900   970  -7.0  -7.2  99  0.2  -7.1 349  24 274.2 274.7 271.8 281.1  2.47  4  850  1420  -2.2  -2.3  99  0.1  -2.3 286  16 283.8 284.5 278.9 294.6  3.80  5  800  1905   0.3   0.1  99  0.2   0.3 237  27 291.5 292.3 283.6 305.5  4.83  6  750  2423  -0.1  -0.5  97  0.4  -0.3 239  38 296.5 297.4 285.7 311.1  4.92  7  700  2975  -1.3  -1.6  98  0.3  -1.4 239  53 301.0 301.9 287.3 315.7  4.88  8  650  3564  -3.1  -3.2  99  0.1  -3.1 237  68 305.5 306.4 288.6 319.7  4.65  9  600  4196  -5.3  -5.4  99  0.1  -5.4 235  78 309.9 310.7 289.8 323.3  4.25 10  550  4876  -8.7  -8.7 100  0.1  -8.7 236  83 313.8 314.5 290.4 325.4  3.60 11  500  5609 -13.0 -13.1  99  0.1 -13.0 242  91 317.2 317.7 290.6 326.3  2.79
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What's different like WXMan1 said is the flow above the cold air advection. It's SW! That's a warm direction. This is an unusual event and there aren't many analogs to compare to. First 5k feet might be screaming northerly and cold and there is a 1 degree speed bump upstairs that cuts totals down

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6Z Thursday at DCA

LEV PRES  HGHT  TEMP  DEWP  RH  DD   WETB DIR SPD THETA THE-V THE-W THE-E   W
     mb     m     C     C    %   C     C  deg knt   K     K     K     K    g/kg
-------------------------------------------------------------------------------
SFC 1010    58   0.4  -0.2  96  0.6   0.2   8  11 272.8 273.4 272.8 282.9  3.74
  1 1000   137  -0.1  -0.6  96  0.5  -0.3   8  16 273.1 273.7 272.9 283.0  3.66
  2  950   546  -2.9  -3.0  99  0.1  -3.0   1  25 274.2 274.7 272.9 283.0  3.21
  3  900   974  -2.3  -2.5  98  0.2  -2.4 324  27 279.1 279.7 276.1 288.9  3.52
  4  850  1430   0.0  -0.1  99  0.1  -0.0 270  18 286.2 286.9 280.8 298.8  4.46
  5  800  1918   1.0   0.7  98  0.3   0.8 241  27 292.2 293.1 284.1 306.7  5.03
  6  750  2437   0.6   0.0  96  0.6   0.3 239  39 297.2 298.1 286.1 312.3  5.10
  7  700  2990  -1.2  -1.3  99  0.2  -1.3 235  49 301.2 302.1 287.5 316.1  4.95
  8  650  3579  -3.1  -3.3  99  0.2  -3.2 229  61 305.4 306.3 288.6 319.6  4.61
  9  600  4211  -5.8  -5.9  99  0.1  -5.8 230  71 309.5 310.2 289.5 322.3  4.11
 10  550  4889  -9.1  -9.2  99  0.1  -9.1 236  77 313.3 314.0 290.1 324.4  3.47
 11  500  5621 -13.3 -13.4  99  0.1 -13.3 244  82 316.9 317.4 290.5 325.8  2.73

Given how marginal and how high up that warm air is...that's a classic sleet profile. As in, what you would see more often in the central part of the U.S.

What bothers me is that there is a real possibility that for a few hours at least I and all the other easterners will be getting pinged while areas N-NW of the District are ripping snow.

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Looks like it flips to sleet around midnight.

The thickness charts scream sleet until perhaps 09Z.  The 1000-850 chart gets that portion of the column under freezing at 03Z but the 1000-500 chart requires until after 09Z to get it done.

 

ERS is gonna suggest go with soundings.  I hear, but I learn slow.

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not really. that would be a terrible way to end winter

 

Yeah, wouldn't be the greatest!  But given a hypothetical choice between all or nearly all rain and a sleetfest...I'd take the sleet.  Of course, would much rather have a short period of sleet while transitioning, then ripping snow the rest of the time.

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What's different like WXMan1 said is the flow above the cold air advection. It's SW! That's a warm direction. This is an unusual event and there aren't many analogs to compare to. First 5k feet might be screaming northerly and cold and there is a 1 degree speed bump upstairs that cuts totals down

Which is why, if anyone has noticed, the 1000-500 mb thicknesses are still >540 DM even while the 850 Ts are tanking. It's that layer within 850-700 mb that's killing us.

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Given how marginal and how high up that warm air is...that's a classic sleet profile. As in, what you would see more often in the central part of the U.S.

What bothers me is that there is a real possibility that for a few hours at least I and all the other easterners will be getting pinged while areas N-NW of the District are ripping snow.

 

There is little doubt that 6z is sleet.  The question is what happens between 6z and 9z and whether 9z is snow (I think it is).  

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The thickness charts scream sleet until perhaps 09Z. The 1000-850 chart gets that portion of the column under freezing at 03Z but the 1000-500 chart requires until after 09Z to get it done.

ERS is gonna suggest go with soundings. I hear, but I learn slow.

Thicknesses are ok. Just another tool in the box but soundings give a better view

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