Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260316_1200
Using the MB925 to MB850 layer.
Assumes Central_Greens are orthogonal to 260 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the Central_Greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Mon 03/16 12Z 0.04 1642  94  98   5 0.00
Mon 03/16 13Z 0.03 1643  96  93   7 0.03
Mon 03/16 14Z 0.08 1742  96  80   8 0.02
Mon 03/16 15Z 0.11 1741  97  62   8 0.02
Mon 03/16 16Z 0.12 1840  96  64   9 0.01
Mon 03/16 18Z 0.28 1941  94  92   9 0.01
Mon 03/16 19Z 0.30 1939  92  77  10 0.01
Mon 03/16 21Z 0.36 1942  97  74  10 0.02
Mon 03/16 22Z 0.33 1844  95  72  11 0.00
Mon 03/16 23Z 0.32 1845  95  77  11 0.01
Tue 03/17 00Z 0.23 1844  95  69  11 0.01
Tue 03/17 01Z 0.15 1743  96  92  10 0.01
Tue 03/17 02Z 0.25 1843  96  92   9 0.01
Tue 03/17 03Z 0.17 1743  97  85   9 0.02
Tue 03/17 04Z 0.16 1745  96  73  10 0.07
Tue 03/17 05Z 0.24 1746  95  88  10 0.04
Tue 03/17 06Z 0.51 1934  98  88   7 0.01
Tue 03/17 07Z 1.67 2534  95  91  -4 0.01
Tue 03/17 08Z 1.23 2534  94  93  -6 0.03
Tue 03/17 09Z 1.85 2530  95   2  -8 0.10
Tue 03/17 10Z 5.85 2531  91   4 -10 0.03
Tue 03/17 11Z 8.34 2433  86  11 -12 0.02
Tue 03/17 12Z 15.35 2438  82  19 -15 0.01
Tue 03/17 13Z 20.62 2436  77  15 -17 0.01
Tue 03/17 14Z 20.16 2433  67  16 -17 0.01
Tue 03/17 15Z 21.33 2531  68  14 -17 0.00
Tue 03/17 16Z 21.03 2530  72   8 -17 0.00
Tue 03/17 17Z 19.41 2528  72   8 -16 0.00
Tue 03/17 18Z 19.05 2527  72  13 -16 0.00
Tue 03/17 19Z 18.57 2526  74  26 -16 0.00
Tue 03/17 20Z 18.43 2627  75  40 -16 0.00
Tue 03/17 21Z 16.45 2627  78  45 -16 0.00
Tue 03/17 22Z 14.41 2626  79  48 -17 0.00
Tue 03/17 23Z 12.56 2726  82  46 -18 0.00
Wed 03/18 00Z 8.14 2726  85  53 -18 0.00
Wed 03/18 01Z 2.90 2725  85  51 -18 0.00
Wed 03/18 02Z 1.57 2724  83  52 -17 0.00
Wed 03/18 03Z 1.02 2724  79  55 -17 0.00
Wed 03/18 04Z 1.36 2724  82  55 -17 0.00
Wed 03/18 05Z 1.28 2724  80  55 -17 0.00
Wed 03/18 06Z 1.48 2725  80  31 -18 0.00
Wed 03/18 07Z 1.77 2725  73  22 -18 0.00
Wed 03/18 08Z 1.38 2725  73  12 -18 0.00
Wed 03/18 09Z 1.26 2825  72   6 -19 0.00
Wed 03/18 10Z 0.99 2823  68   5 -19 0.00
Wed 03/18 11Z 0.67 2920  64   4 -19 0.00
Wed 03/18 12Z 0.49 2917  63   4 -18 0.00
Wed 03/18 13Z 0.37 2913  59   5 -18 0.00
Wed 03/18 14Z 0.36 2811  55   5 -18 0.00
Wed 03/18 15Z 0.31 2708  45   6 -17 0.00
Wed 03/18 16Z 0.50 2607  41   7 -16 0.00
Wed 03/18 17Z 0.86 2505  38   7 -16 0.00
Wed 03/18 18Z 0.80 2304  35   7 -15 0.00
Wed 03/18 19Z 0.92 2303  33   7 -14 0.00
Wed 03/18 20Z 0.73 2203  32   8 -13 0.00
Wed 03/18 21Z 0.58 2005  31   7 -13 0.00
Wed 03/18 22Z 0.28 1907  32   9 -12 0.00
Wed 03/18 23Z 0.17 1809  33   9 -12 0.00

Run total areal avg QPF for the Central_Greens is: 0.52 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