NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260131_0600
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sat 01/31 06Z 0.15 3214  79  37 -16 0.00
Sat 01/31 07Z 0.18 3117  79  38 -15 0.00
Sat 01/31 08Z 0.17 3116  79  38 -15 0.00
Sat 01/31 09Z 0.16 3216  78  38 -15 0.00
Sat 01/31 11Z 0.15 3215  78  36 -15 0.00
Sat 01/31 12Z 0.15 3215  78  34 -15 0.00
Sat 01/31 13Z 0.13 3215  79  32 -15 0.00
Sat 01/31 14Z 0.11 3314  79  30 -15 0.00
Sat 01/31 15Z 0.09 3312  79  28 -15 0.00
Sat 01/31 16Z 0.09 3210  79  27 -14 0.00
Sat 01/31 18Z 0.11 3209  77  25 -14 0.00
Sat 01/31 19Z 0.10 3208  76  25 -14 0.00
Sat 01/31 20Z 0.11 3209  74  25 -14 0.00
Sat 01/31 21Z 0.10 3210  73  25 -14 0.00
Sat 01/31 22Z 0.09 3310  73  25 -14 0.00
Sat 01/31 23Z 0.09 3312  73  26 -14 0.00
Sun 02/01 00Z 0.08 3414  73  26 -13 0.00
Sun 02/01 01Z 0.05 3415  73  27 -12 0.00
Sun 02/01 02Z 0.02 3514  74  26 -12 0.00
Sun 02/01 03Z 0.03 0014  74  26 -12 0.00
Sun 02/01 04Z 0.04 0113  74  27 -12 0.00
Sun 02/01 05Z 0.06 0112  73  26 -11 0.00
Sun 02/01 06Z 0.08 0212  70  25 -11 0.00
Sun 02/01 07Z 0.08 0212  66  24 -10 0.00
Sun 02/01 08Z 0.07 0211  64  24 -10 0.00
Sun 02/01 09Z 0.08 0212  64  23 -10 0.00
Sun 02/01 10Z 0.09 0213  64  23 -10 0.00
Sun 02/01 11Z 0.10 0216  62  22  -9 0.00
Sun 02/01 12Z 0.12 0217  63  23 -10 0.00
Sun 02/01 13Z 0.09 0216  65  25 -10 0.00
Sun 02/01 14Z 0.13 0317  66  24 -10 0.00
Sun 02/01 15Z 0.12 0217  64  22 -10 0.00
Sun 02/01 16Z 0.13 0217  63  19  -9 0.00
Sun 02/01 17Z 0.12 0217  65  19  -9 0.00
Sun 02/01 18Z 0.12 0217  66  18  -9 0.00
Sun 02/01 19Z 0.13 0219  64  17  -8 0.00
Sun 02/01 20Z 0.10 0120  66  16  -8 0.00
Sun 02/01 21Z 0.08 0122  68  16  -8 0.00
Sun 02/01 22Z 0.07 0125  67  16  -8 0.00
Sun 02/01 23Z 0.10 0126  67  16  -8 0.00
Mon 02/02 00Z 0.11 0127  70  16  -9 0.00
Mon 02/02 01Z 0.11 0127  71  15  -9 0.00
Mon 02/02 02Z 0.10 0127  72  13  -8 0.00
Mon 02/02 03Z 0.07 0027  74  14  -9 0.00
Mon 02/02 04Z 0.08 0028  77  14  -9 0.00
Mon 02/02 05Z 0.04 0027  76  15  -9 0.00
Mon 02/02 06Z 0.04 0026  74  15  -9 0.00
Mon 02/02 07Z 0.04 0025  75  16  -9 0.00
Mon 02/02 08Z 0.03 0024  73  17  -9 0.00
Mon 02/02 09Z 0.03 3523  73  17  -9 0.00
Mon 02/02 10Z 0.03 3522  73  17  -8 0.00
Mon 02/02 11Z 0.03 3522  73  17  -8 0.00
Mon 02/02 12Z 0.03 3522  74  18  -8 0.00
Mon 02/02 13Z 0.03 3521  74  19  -8 0.00
Mon 02/02 14Z 0.04 3519  72  19  -8 0.00
Mon 02/02 15Z 0.05 3418  72  19  -8 0.00
Mon 02/02 16Z 0.06 3417  71  21  -8 0.00

Run total areal avg QPF for the greens is: 0.00 inches.

Froude Number (Frd#): 
Frd# < 0.5 Flow is subcritical and blocked.
         Upslope clouds/precip backed farther upwind of and up to mtn crest.
         W Upslope snow favors eastern Champlain Valley, BTV, and Western slopes.
         Gap winds possible.
Frd# 0.5-1 Flow is subcritical/slow moving/blocked.
         Upslope clouds/precip falls immediately upwind of mtn crest.
         W Upslope snow favors western slopes to the Green Mt. spine including:
         Montgomery,Underhill,Jericho,Bolton,Richmond,Huntington,Lincoln.
         Gap winds possible.
Frd# 1-2 Flow is critical.
         With strong winds, Mountain waves/downslope winds possible.
         Precip falls close to mountain ridge crests and on lee side.
         W Upslope snow favors Green Mt Spine,Jay,Stowe,Waterbury,NE Kingdom.
Froude > 2 Flow is supercritical/unblocked(rapid flow).
         Air flows freely over terrain.
         Persistent upslope snow not favored. Scattered snow showers and flurries.

Relative Humidity (RH): 
         925-850 mb RH > 90% needed for upslope precipitation.
         with 700mb RH > 70% favors upslope snow.
         with 700mb RH > 90% greater amounts of W upslope snow possible.

850mb Temperature (T degC) Westerly Upslope Snow Ratios: (Avg=28:1)
        T > -11       10-15:1
        T -11 to -15  25-35:1
        T < -15       15-20:1