NAM3 EXPERIMENTAL Froude Number for the Northern Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Northern_Greens

Model run: BTV_GRID_D2D_NAM3_20251007_1800
Using the MB925 to MB850 layer.
Assumes Northern_Greens are orthogonal to 290 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Northern_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Tue 10/07 18Z 0.25 2019  72  94  13 0.00
Tue 10/07 19Z 0.65 2124  76  95  13 0.00
Tue 10/07 20Z 0.57 2228  92  93  12 0.04
Tue 10/07 21Z 0.50 2329  81  87  12 0.10
Tue 10/07 22Z 0.49 2328  78  87  13 0.05
Tue 10/07 23Z 0.63 2329  78  83  13 0.00
Wed 10/08 00Z 0.44 2226  87  76  12 0.00
Wed 10/08 01Z 0.29 2128  95  91  12 0.03
Wed 10/08 02Z 0.17 2130  98  96  12 0.10
Wed 10/08 03Z 0.34 2133  97  92  12 0.40
Wed 10/08 04Z 0.38 2323  99  94  12 0.43
Wed 10/08 05Z 0.28 3422  97  92  10 0.47
Wed 10/08 06Z 0.23 3417  95  96   9 0.03
Wed 10/08 07Z 0.24 3414  83  98   8 0.03
Wed 10/08 08Z 0.21 3415  74  98   7 0.02
Wed 10/08 09Z 0.16 3513  88  98   6 0.07
Wed 10/08 10Z 0.17 3413  87  98   6 0.06
Wed 10/08 11Z 0.21 3516  90  99   5 0.08
Wed 10/08 12Z 0.15 0016  91  98   5 0.09
Wed 10/08 13Z 0.22 3518  93  96   4 0.05
Wed 10/08 14Z 0.28 3519  87  93   3 0.01
Wed 10/08 15Z 0.32 3522  71  94   3 0.01
Wed 10/08 16Z 0.38 3522  71  77   2 0.00
Wed 10/08 17Z 0.58 3422  81  44   1 0.00
Wed 10/08 18Z 0.69 3422  89  19   1 0.00
Wed 10/08 19Z 0.69 3422  91   1   1 0.00
Wed 10/08 20Z 0.71 3421  92   2   0 0.01
Wed 10/08 21Z 0.68 3422  91   3   0 0.00
Wed 10/08 22Z 0.63 3424  84   5   0 0.00
Wed 10/08 23Z 0.64 3426  77   8   0 0.00
Thu 10/09 00Z 0.72 3427  85   8  -1 0.00
Thu 10/09 01Z 0.88 3426  90   6  -2 0.00
Thu 10/09 02Z 0.79 3425  93   8  -2 0.00
Thu 10/09 03Z 0.58 3423  92   7  -3 0.00
Thu 10/09 04Z 0.50 3422  90   9  -3 0.00
Thu 10/09 05Z 0.44 3422  81  15  -4 0.00
Thu 10/09 06Z 0.38 3423  69  10  -3 0.00
Thu 10/09 07Z 0.36 3424  69  14  -4 0.00
Thu 10/09 08Z 0.37 3423  70  16  -5 0.00
Thu 10/09 09Z 0.38 3424  74  17  -5 0.00
Thu 10/09 10Z 0.41 3424  79  17  -6 0.00
Thu 10/09 11Z 0.42 3423  78  15  -6 0.01
Thu 10/09 12Z 0.40 3424  78  13  -6 0.00
Thu 10/09 13Z 0.40 3424  81   9  -6 0.00
Thu 10/09 14Z 0.38 3423  82   7  -6 0.00
Thu 10/09 15Z 0.40 3421  80   5  -6 0.00
Thu 10/09 16Z 0.44 3319  82   6  -6 0.00
Thu 10/09 17Z 0.53 3318  81   5  -6 0.00
Thu 10/09 18Z 0.56 3316  78   6  -5 0.00
Thu 10/09 19Z 0.59 3315  74   8  -5 0.00
Thu 10/09 20Z 0.54 3215  69   9  -4 0.00
Thu 10/09 21Z 0.46 3214  64   9  -4 0.00
Thu 10/09 22Z 0.44 3216  58   8  -3 0.00
Thu 10/09 23Z 0.44 3217  52   8  -2 0.00
Fri 10/10 00Z 0.47 3117  51   8  -2 0.00
Fri 10/10 01Z 0.47 3117  49   9  -1 0.00
Fri 10/10 02Z 0.43 3117  45  11  -1 0.00
Fri 10/10 03Z 0.40 3116  42  14  -1 0.00
Fri 10/10 04Z 0.38 3015  41  13   0 0.00
Fri 10/10 05Z 0.36 3014  38  11   0 0.00

Run total areal avg QPF for the Northern_Greens is: 2.09 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