NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260213_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)
=== ===== === ==== ==== === === === ====
Fri 02/13 06Z 0.10 3416  75  26 -11 0.00
Fri 02/13 07Z 0.13 3316  75  27 -11 0.00
Fri 02/13 08Z 0.15 3316  72  29 -10 0.00
Fri 02/13 09Z 0.16 3315  69  32 -10 0.00
Fri 02/13 10Z 0.19 3216  67  33  -9 0.00
Fri 02/13 11Z 0.22 3117  66  32  -9 0.00
Fri 02/13 12Z 0.23 3117  65  29  -9 0.00
Fri 02/13 13Z 0.24 3117  66  26  -9 0.00
Fri 02/13 14Z 0.24 3117  67  25  -9 0.00
Fri 02/13 15Z 0.25 3016  68  25  -9 0.00
Fri 02/13 16Z 0.27 2915  68  24  -9 0.00
Fri 02/13 17Z 0.31 2916  66  24 -10 0.00
Fri 02/13 18Z 0.34 2915  61  25 -10 0.00
Fri 02/13 19Z 0.35 2915  58  22 -10 0.00
Fri 02/13 20Z 0.38 2815  60  23 -10 0.00
Fri 02/13 21Z 0.42 2716  65  38 -10 0.00
Fri 02/13 23Z 0.48 2718  64  59 -10 0.00
Sat 02/14 00Z 0.50 2719  62  48 -10 0.00
Sat 02/14 01Z 0.42 2718  54  41  -9 0.00
Sat 02/14 02Z 0.36 2717  47  46  -8 0.00
Sat 02/14 03Z 0.37 2718  52  50  -9 0.00
Sat 02/14 04Z 0.40 2719  60  47  -9 0.00
Sat 02/14 05Z 0.39 2718  62  64  -9 0.00
Sat 02/14 06Z 0.41 2718  70  76  -9 0.00
Sat 02/14 07Z 0.42 2718  90  78 -10 0.00
Sat 02/14 08Z 0.43 2717  92  83 -10 0.00
Sat 02/14 09Z 0.46 2718  93  81 -10 0.00
Sat 02/14 10Z 0.46 2718  93  84 -10 0.00
Sat 02/14 11Z 0.50 2819  93  88 -10 0.01
Sat 02/14 12Z 0.54 2820  94  85 -10 0.01
Sat 02/14 13Z 0.58 2821  95  79 -10 0.01
Sat 02/14 14Z 0.61 2922  95  59 -11 0.01
Sat 02/14 15Z 0.59 2921  95  36 -11 0.01
Sat 02/14 16Z 0.59 3021  94  17 -11 0.01
Sat 02/14 17Z 0.65 3020  84  18 -11 0.01
Sat 02/14 18Z 0.68 2919  75  20 -11 0.00
Sat 02/14 19Z 0.74 2919  76  26 -11 0.00
Sat 02/14 20Z 0.82 2820  78  29 -11 0.00
Sat 02/14 21Z 1.01 2822  78  30 -12 0.00
Sat 02/14 22Z 1.17 2925  74  32 -12 0.00
Sat 02/14 23Z 1.44 2928  70  33 -13 0.00
Sun 02/15 00Z 1.51 3029  67  26 -13 0.00
Sun 02/15 01Z 1.45 3030  68  22 -14 0.00
Sun 02/15 02Z 1.34 3130  72  19 -15 0.00
Sun 02/15 03Z 1.25 3129  78  20 -16 0.00
Sun 02/15 04Z 0.90 3228  80  17 -16 0.00
Sun 02/15 05Z 0.55 3226  74  13 -16 0.00
Sun 02/15 06Z 0.33 3325  62  12 -15 0.00
Sun 02/15 07Z 0.23 3324  49  12 -14 0.00
Sun 02/15 08Z 0.15 3421  39  10 -13 0.00
Sun 02/15 09Z 0.10 3419  30  10 -12 0.00
Sun 02/15 10Z 0.06 3516  23  13 -11 0.00
Sun 02/15 11Z 0.03 3513  20  16 -10 0.00
Sun 02/15 12Z 0.02 3511  18  16  -9 0.00
Sun 02/15 13Z 0.02 3508  18  17  -9 0.00
Sun 02/15 14Z 0.02 3505  18  19  -8 0.00
Sun 02/15 15Z 0.02 3403  19  22  -8 0.00
Sun 02/15 16Z 0.02 3401  21  32  -7 0.00
Sun 02/15 17Z 0.04 2501  24  53  -7 0.00

Run total areal avg QPF for the greens is: 0.07 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