NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260527_1200
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 12Z 0.51 2916  77  43  11 0.00
Wed 05/27 13Z 0.47 2914  79  39  11 0.00
Wed 05/27 14Z 0.49 2912  78  37  10 0.00
Wed 05/27 15Z 0.58 2911  76  33  10 0.00
Wed 05/27 16Z 1.25 2911  76  28  10 0.00
Wed 05/27 17Z 2.86 3011  76  27  10 0.00
Wed 05/27 18Z 2.02 3012  81  29  10 0.00
Wed 05/27 19Z 1.34 3112  82  29  10 0.01
Wed 05/27 20Z 1.56 3114  81  28   9 0.00
Wed 05/27 21Z 1.62 3214  79  23   9 0.00
Wed 05/27 22Z 1.15 3315  78  22   9 0.00
Wed 05/27 23Z 0.60 3316  80  22   8 0.00
Thu 05/28 00Z 0.42 3317  84  33   7 0.00
Thu 05/28 01Z 0.28 3418  91  47   7 0.01
Thu 05/28 02Z 0.21 3419  90  51   6 0.01
Thu 05/28 03Z 0.13 3518  92  47   6 0.00
Thu 05/28 04Z 0.10 3518  92  49   6 0.00
Thu 05/28 05Z 0.06 0017  92  57   5 0.00
Thu 05/28 06Z 0.04 3517  91  69   5 0.00
Thu 05/28 07Z 0.12 3517  91  66   5 0.00
Thu 05/28 08Z 0.15 3418  92  64   4 0.00
Thu 05/28 09Z 0.17 3418  92  59   4 0.00
Thu 05/28 10Z 0.20 3419  90  61   4 0.00
Thu 05/28 11Z 0.21 3420  89  66   4 0.00
Thu 05/28 12Z 0.18 3420  91  70   4 0.01
Thu 05/28 13Z 0.17 3419  94  70   3 0.01
Thu 05/28 14Z 0.24 3419  96  72   3 0.01
Thu 05/28 15Z 0.33 3418  96  72   3 0.01
Thu 05/28 16Z 0.43 3419  96  72   3 0.01
Thu 05/28 17Z 0.56 3319  95  70   3 0.01
Thu 05/28 18Z 0.66 3321  92  72   3 0.01
Thu 05/28 19Z 0.99 3321  92  73   3 0.01
Thu 05/28 20Z 1.39 3321  91  69   3 0.01
Thu 05/28 21Z 1.16 3320  93  73   3 0.01
Thu 05/28 22Z 0.55 3323  92  68   3 0.02
Thu 05/28 23Z 0.49 3326  94  56   3 0.02
Fri 05/29 00Z 0.45 3327  92  45   3 0.01
Fri 05/29 01Z 0.34 3425  95  32   3 0.01
Fri 05/29 02Z 0.38 3426  95  28   2 0.01
Fri 05/29 03Z 0.37 3425  95  30   2 0.01
Fri 05/29 04Z 0.33 3424  96  32   2 0.01
Fri 05/29 05Z 0.30 3422  96  32   2 0.01
Fri 05/29 06Z 0.27 3420  98  41   2 0.01
Fri 05/29 07Z 0.33 3319  98  65   2 0.02
Fri 05/29 08Z 0.39 3320  96  79   1 0.01
Fri 05/29 09Z 0.38 3220  95  77   1 0.00
Fri 05/29 10Z 0.37 3220  91  78   2 0.00
Fri 05/29 11Z 0.35 3221  88  80   2 0.00
Fri 05/29 12Z 0.34 3322  86  80   2 0.00
Fri 05/29 13Z 0.37 3219  83  81   2 0.00
Fri 05/29 14Z 0.54 3117  80  78   2 0.00
Fri 05/29 15Z 1.45 3116  74  78   2 0.00
Fri 05/29 16Z 4.42 3013  73  76   3 0.00
Fri 05/29 17Z 5.17 2911  73  81   4 0.00
Fri 05/29 18Z 5.16 2709  70  89   4 0.00
Fri 05/29 19Z 5.72 2612  72  97   5 0.00
Fri 05/29 20Z 3.95 2612  71  83   5 0.01
Fri 05/29 21Z 4.34 2511  71  91   5 0.00
Fri 05/29 22Z 1.64 2214  75  82   5 0.01
Fri 05/29 23Z 0.89 2319  79  87   5 0.01

Run total areal avg QPF for the greens is: 0.30 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