Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260208_0000
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Sun 02/08 00Z 0.17 3321  80  59 -23 0.00
Sun 02/08 01Z 0.22 3225  81  57 -22 0.00
Sun 02/08 02Z 0.22 3226  80  55 -22 0.00
Sun 02/08 03Z 0.17 3326  77  55 -22 0.00
Sun 02/08 04Z 0.13 3326  78  55 -21 0.00
Sun 02/08 05Z 0.12 3325  80  55 -21 0.00
Sun 02/08 06Z 0.11 3324  79  58 -21 0.00
Sun 02/08 07Z 0.10 3323  77  61 -20 0.00
Sun 02/08 08Z 0.08 3323  76  64 -20 0.00
Sun 02/08 09Z 0.07 3323  76  66 -20 0.00
Sun 02/08 10Z 0.07 3323  77  67 -20 0.00
Sun 02/08 11Z 0.07 3324  78  66 -19 0.00
Sun 02/08 12Z 0.05 3425  78  65 -19 0.00
Sun 02/08 13Z 0.03 3425  78  69 -19 0.00
Sun 02/08 14Z 0.03 3425  76  68 -18 0.00
Sun 02/08 15Z 0.02 3425  76  52 -18 0.00
Sun 02/08 16Z 0.03 3425  75  49 -17 0.00
Sun 02/08 17Z 0.03 3425  74  52 -17 0.00
Sun 02/08 18Z 0.03 3424  71  36 -16 0.00
Sun 02/08 19Z 0.03 3425  65  35 -14 0.00
Sun 02/08 20Z 0.03 3425  64  42 -14 0.00
Sun 02/08 21Z 0.03 3426  64  46 -13 0.00
Sun 02/08 22Z 0.03 3427  64  44 -12 0.00
Sun 02/08 23Z 0.03 3528  65  47 -12 0.00
Mon 02/09 00Z 0.03 3429  69  44 -12 0.00
Mon 02/09 01Z 0.02 3429  68  33 -12 0.00
Mon 02/09 02Z 0.03 3429  66  26 -12 0.00
Mon 02/09 03Z 0.05 3429  63  27 -11 0.00
Mon 02/09 04Z 0.07 3430  63  33 -11 0.00
Mon 02/09 05Z 0.08 3331  61  38 -11 0.00
Mon 02/09 06Z 0.10 3332  59  36 -12 0.00
Mon 02/09 07Z 0.11 3333  63  32 -12 0.00
Mon 02/09 08Z 0.11 3333  66  29 -12 0.00
Mon 02/09 09Z 0.11 3333  65  25 -12 0.00
Mon 02/09 10Z 0.11 3334  65  23 -12 0.00
Mon 02/09 11Z 0.10 3334  64  21 -12 0.00
Mon 02/09 12Z 0.07 3434  59  17 -12 0.00
Mon 02/09 13Z 0.06 3435  57  13 -12 0.00
Mon 02/09 14Z 0.05 3434  55  10 -11 0.00
Mon 02/09 15Z 0.04 3432  53   8 -11 0.00
Mon 02/09 16Z 0.06 3431  52  11 -11 0.00
Mon 02/09 17Z 0.07 3429  49  22 -11 0.00
Mon 02/09 18Z 0.11 3328  49  38 -12 0.00
Mon 02/09 19Z 0.11 3328  47  52 -11 0.00
Mon 02/09 20Z 0.12 3326  44  55 -11 0.00
Mon 02/09 21Z 0.11 3325  41  49 -10 0.00
Mon 02/09 22Z 0.12 3326  40  48  -9 0.00
Mon 02/09 23Z 0.13 3326  37  52  -9 0.00
Tue 02/10 00Z 0.10 3325  34  54  -8 0.00
Tue 02/10 01Z 0.08 3325  30  56  -8 0.00
Tue 02/10 02Z 0.07 3424  24  57  -8 0.00
Tue 02/10 03Z 0.06 3423  21  64  -8 0.00
Tue 02/10 04Z 0.05 3420  19  61  -8 0.00
Tue 02/10 05Z 0.04 3418  17  61  -7 0.00
Tue 02/10 06Z 0.08 3318  17  70  -7 0.00
Tue 02/10 07Z 0.09 3317  17  67  -7 0.00
Tue 02/10 08Z 0.12 3216  18  68  -7 0.00
Tue 02/10 09Z 0.11 3214  18  70  -7 0.00
Tue 02/10 10Z 0.12 3112  19  75  -7 0.00
Tue 02/10 11Z 0.10 3110  20  72  -7 0.00

Run total areal avg QPF for the Central_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