NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260906_0000
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)
=== ===== === ==== ==== === === === ====
Sun 09/06 00Z 0.28 0312  93  85   8 0.00
Sun 09/06 01Z 0.39 0413  94  82   8 0.01
Sun 09/06 02Z 0.44 0613  94  83   8 0.01
Sun 09/06 03Z 0.43 0712  95  87   8 0.01
Sun 09/06 04Z 0.40 0911  93  93   7 0.01
Sun 09/06 05Z 0.32 1008  93  90   7 0.01
Sun 09/06 06Z 0.22 1006  92  83   7 0.01
Sun 09/06 07Z 0.18 0904  94  84   7 0.01
Sun 09/06 08Z 0.14 0704  95  91   7 0.01
Sun 09/06 09Z 0.13 0504  95  90   7 0.02
Sun 09/06 10Z 0.15 0405  95  90   6 0.02
Sun 09/06 11Z 0.16 0406  94  88   6 0.05
Sun 09/06 12Z 0.13 0207  93  84   6 0.05
Sun 09/06 13Z 0.12 0209  92  77   6 0.02
Sun 09/06 14Z 0.12 0110  91  71   6 0.01
Sun 09/06 15Z 0.10 0110  91  60   6 0.00
Sun 09/06 16Z 0.08 0010  91  56   6 0.00
Sun 09/06 17Z 0.10 0010  90  47   6 0.00
Sun 09/06 18Z 0.13 3511  90  34   6 0.00
Sun 09/06 19Z 0.29 3512  89  24   7 0.00
Sun 09/06 20Z 0.43 3412  90  17   7 0.00
Sun 09/06 21Z 0.25 3413  91  16   7 0.01
Sun 09/06 22Z 0.21 3415  89  26   7 0.01
Sun 09/06 23Z 0.23 3417  86  26   7 0.00
Mon 09/07 00Z 0.21 3420  81  21   7 0.00
Mon 09/07 01Z 0.28 3421  84  22   7 0.00
Mon 09/07 02Z 0.30 3422  89  23   7 0.01
Mon 09/07 03Z 0.28 3423  89  16   7 0.01
Mon 09/07 04Z 0.19 3423  88  15   7 0.00
Mon 09/07 05Z 0.17 3422  89  15   6 0.00
Mon 09/07 06Z 0.26 3421  87  14   6 0.00
Mon 09/07 07Z 0.19 3421  85  14   6 0.00
Mon 09/07 08Z 0.17 3420  82  15   6 0.00
Mon 09/07 09Z 0.14 3419  76  15   7 0.00
Mon 09/07 10Z 0.23 3419  77  14   7 0.00
Mon 09/07 11Z 0.32 3320  76  15   7 0.00
Mon 09/07 12Z 0.34 3320  74  15   7 0.00
Mon 09/07 13Z 0.33 3319  74  13   7 0.00
Mon 09/07 14Z 0.37 3319  74  11   7 0.00
Mon 09/07 15Z 0.49 3320  76  11   7 0.00
Mon 09/07 16Z 1.27 3319  78  10   7 0.00
Mon 09/07 17Z 4.51 3217  82   9   7 0.00
Mon 09/07 18Z 3.64 3115  84   8   7 0.00
Mon 09/07 19Z 3.57 3115  84   7   7 0.00
Mon 09/07 20Z 2.52 3015  81   7   8 0.00
Mon 09/07 21Z 1.65 3016  80  13   8 0.00
Mon 09/07 22Z 1.17 3017  80  29   8 0.00
Mon 09/07 23Z 0.92 3019  79  47   9 0.00
Tue 09/08 00Z 0.72 3020  77  57   9 0.00
Tue 09/08 01Z 0.69 3021  77  61   9 0.00
Tue 09/08 02Z 0.60 3021  78  64   9 0.00
Tue 09/08 03Z 0.57 3021  80  65  10 0.00
Tue 09/08 04Z 0.58 3022  82  72  10 0.00
Tue 09/08 05Z 0.56 3022  85  81   9 0.01
Tue 09/08 06Z 0.52 3021  87  82  10 0.03
Tue 09/08 07Z 0.44 3120  90  82  10 0.06
Tue 09/08 08Z 0.38 3120  93  77  10 0.04
Tue 09/08 09Z 0.35 3220  95  74   9 0.03
Tue 09/08 10Z 0.30 3220  92  66   9 0.02
Tue 09/08 11Z 0.21 3320  84  48   9 0.01

Run total areal avg QPF for the greens is: 0.49 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