NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260213_1800
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 18Z 0.31 3010  83   8 -11 0.00
Fri 02/13 19Z 0.36 2912  78  11 -10 0.00
Fri 02/13 20Z 0.37 2812  74  18 -10 0.00
Fri 02/13 21Z 0.45 2714  79  38 -10 0.00
Fri 02/13 22Z 0.53 2716  82  50 -10 0.00
Fri 02/13 23Z 0.64 2618  83  49 -10 0.00
Sat 02/14 00Z 0.65 2619  80  48 -10 0.00
Sat 02/14 01Z 0.57 2619  72  52 -10 0.00
Sat 02/14 02Z 0.48 2619  62  52  -9 0.00
Sat 02/14 03Z 0.44 2618  55  50  -9 0.00
Sat 02/14 04Z 0.44 2619  56  41  -9 0.00
Sat 02/14 05Z 0.43 2619  55  51  -9 0.00
Sat 02/14 06Z 0.42 2619  54  77  -9 0.00
Sat 02/14 07Z 0.41 2718  72  79  -9 0.00
Sat 02/14 08Z 0.44 2718  91  82  -9 0.01
Sat 02/14 09Z 0.50 2719  93  76 -10 0.01
Sat 02/14 10Z 0.51 2720  93  83  -9 0.00
Sat 02/14 11Z 0.52 2719  93  88  -9 0.01
Sat 02/14 12Z 0.53 2819  94  81  -9 0.01
Sat 02/14 13Z 0.55 2819  95  75  -9 0.01
Sat 02/14 14Z 0.57 2819  96  67 -10 0.01
Sat 02/14 15Z 0.59 2819  96  56 -10 0.01
Sat 02/14 16Z 0.60 2918  96  44 -10 0.01
Sat 02/14 17Z 0.65 2917  96  34 -10 0.00
Sat 02/14 18Z 0.80 2918  96  28 -10 0.00
Sat 02/14 19Z 1.02 2818  97  23 -10 0.01
Sat 02/14 20Z 1.07 2919  94  18 -10 0.01
Sat 02/14 21Z 0.98 2919  89  18 -10 0.00
Sat 02/14 22Z 0.87 2921  85  18 -10 0.01
Sat 02/14 23Z 0.81 2922  83  20 -11 0.01
Sun 02/15 00Z 0.73 3022  80  23 -11 0.01
Sun 02/15 02Z 0.90 3025  75  17 -12 0.00
Sun 02/15 03Z 0.86 3026  75  15 -12 0.00
Sun 02/15 04Z 0.81 3127  77  14 -12 0.00
Sun 02/15 05Z 0.62 3127  76  13 -13 0.00
Sun 02/15 06Z 0.48 3227  72  12 -13 0.00
Sun 02/15 07Z 0.38 3226  64  14 -12 0.00
Sun 02/15 08Z 0.31 3225  57  14 -12 0.00
Sun 02/15 09Z 0.24 3324  50  14 -11 0.00
Sun 02/15 10Z 0.17 3323  41  14 -11 0.00
Sun 02/15 11Z 0.14 3421  35  14 -10 0.00
Sun 02/15 12Z 0.10 3418  30  15 -10 0.00
Sun 02/15 13Z 0.06 3415  25  15  -9 0.00
Sun 02/15 14Z 0.02 3512  21  16  -9 0.00
Sun 02/15 15Z 0.02 0008  20  17  -8 0.00
Sun 02/15 16Z 0.03 0105  22  20  -8 0.00
Sun 02/15 17Z 0.03 0103  25  25  -7 0.00
Sun 02/15 18Z 0.02 0200  28  35  -7 0.00
Sun 02/15 19Z 0.02 1400  30  46  -7 0.00
Sun 02/15 20Z 0.04 2003  33  54  -7 0.00
Sun 02/15 21Z 0.05 2004  34  55  -6 0.00
Sun 02/15 22Z 0.07 2006  33  50  -6 0.00
Sun 02/15 23Z 0.10 2008  32  52  -6 0.00
Mon 02/16 02Z 0.17 2112  35  75  -6 0.00
Mon 02/16 03Z 0.16 2112  42  82  -6 0.00
Mon 02/16 04Z 0.17 2112  49  78  -6 0.00
Mon 02/16 05Z 0.18 2112  54  81  -5 0.00

Run total areal avg QPF for the greens is: 0.13 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