NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260527_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)
=== ===== === ==== ==== === === === ====
Wed 05/27 06Z 1.12 2732  64  59  13 0.00
Wed 05/27 07Z 1.12 2832  65  52  13 0.00
Wed 05/27 08Z 0.97 2830  70  45  13 0.00
Wed 05/27 09Z 0.80 2827  77  44  12 0.00
Wed 05/27 10Z 0.68 2824  80  43  12 0.00
Wed 05/27 11Z 0.56 2921  82  43  12 0.00
Wed 05/27 12Z 0.46 2918  80  50  11 0.00
Wed 05/27 13Z 0.40 3016  78  40  11 0.00
Wed 05/27 14Z 0.41 3014  77  30  10 0.00
Wed 05/27 15Z 0.48 3013  77  28  10 0.00
Wed 05/27 16Z 0.86 2913  77  21   9 0.00
Wed 05/27 17Z 2.09 2913  79  18   9 0.00
Wed 05/27 18Z 2.97 2913  82  15   9 0.00
Wed 05/27 19Z 2.16 3013  83  16   9 0.00
Wed 05/27 20Z 1.43 3114  81  16   9 0.00
Wed 05/27 21Z 1.31 3215  78  18   9 0.00
Wed 05/27 22Z 1.07 3216  81  24   8 0.00
Wed 05/27 23Z 0.58 3318  83  26   8 0.00
Thu 05/28 00Z 0.39 3320  87  32   7 0.00
Thu 05/28 01Z 0.30 3420  88  31   6 0.01
Thu 05/28 02Z 0.20 3420  90  31   6 0.00
Thu 05/28 03Z 0.19 3419  92  42   5 0.00
Thu 05/28 04Z 0.17 3518  91  47   5 0.00
Thu 05/28 05Z 0.17 3418  92  49   4 0.00
Thu 05/28 06Z 0.23 3418  89  54   4 0.00
Thu 05/28 07Z 0.18 3419  90  62   4 0.00
Thu 05/28 08Z 0.19 3419  90  60   4 0.00
Thu 05/28 09Z 0.19 3419  90  65   4 0.00
Thu 05/28 10Z 0.21 3420  91  67   3 0.00
Thu 05/28 11Z 0.26 3421  90  69   3 0.00
Thu 05/28 12Z 0.26 3320  89  65   3 0.00
Thu 05/28 13Z 0.32 3318  91  67   3 0.01
Thu 05/28 14Z 0.46 3418  92  70   3 0.01
Thu 05/28 15Z 0.55 3419  92  75   3 0.01
Thu 05/28 16Z 0.60 3419  93  78   3 0.01
Thu 05/28 17Z 0.48 3320  94  81   3 0.01
Thu 05/28 18Z 0.77 3321  93  79   3 0.01
Thu 05/28 19Z 1.03 3320  92  73   3 0.01
Thu 05/28 20Z 1.40 3320  91  66   3 0.01
Thu 05/28 21Z 0.90 3319  89  58   3 0.01
Thu 05/28 22Z 0.75 3320  91  59   4 0.02
Thu 05/28 23Z 0.45 3323  93  56   4 0.02
Fri 05/29 00Z 0.35 3425  93  55   3 0.02
Fri 05/29 01Z 0.30 3425  93  52   3 0.01
Fri 05/29 02Z 0.24 3423  95  45   3 0.01
Fri 05/29 03Z 0.22 3422  96  35   3 0.01
Fri 05/29 04Z 0.20 3422  96  30   2 0.01
Fri 05/29 05Z 0.16 3421  96  29   2 0.01
Fri 05/29 06Z 0.17 3420  96  36   2 0.01
Fri 05/29 07Z 0.20 3420  97  47   2 0.01
Fri 05/29 08Z 0.19 3419  95  76   2 0.00
Fri 05/29 09Z 0.23 3419  94  72   2 0.00
Fri 05/29 10Z 0.28 3319  93  68   2 0.00
Fri 05/29 11Z 0.30 3318  87  70   2 0.00
Fri 05/29 12Z 0.34 3217  82  79   2 0.00
Fri 05/29 13Z 0.33 3116  78  85   3 0.00
Fri 05/29 14Z 0.42 3115  75  84   3 0.00
Fri 05/29 15Z 0.68 3014  72  78   3 0.00
Fri 05/29 16Z 3.41 2912  76  79   3 0.00
Fri 05/29 17Z 5.88 2711  78  82   4 0.00

Run total areal avg QPF for the greens is: 0.23 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