Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260404_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)
=== ===== === ==== ==== === === === ====
Sat 04/04 12Z 0.05 3513  79  15   4 0.00
Sat 04/04 13Z 0.09 0210  71  13   5 0.00
Sat 04/04 14Z 0.13 0409  66  11   5 0.00
Sat 04/04 15Z 0.14 0708  63  15   6 0.00
Sat 04/04 16Z 0.13 1108  65  25   5 0.00
Sat 04/04 17Z 0.14 1311  73  43   4 0.00
Sat 04/04 18Z 0.15 1414  81  54   3 0.00
Sat 04/04 19Z 0.21 1417  85  58   3 0.00
Sat 04/04 20Z 0.21 1520  90  71   2 0.00
Sat 04/04 21Z 0.19 1524  88  86   3 0.01
Sat 04/04 22Z 0.15 1525  80  95   5 0.00
Sat 04/04 23Z 0.12 1528  75  97   5 0.00
Sun 04/05 00Z 0.09 1629  85  89   5 0.02
Sun 04/05 01Z 0.05 1630  91  91   6 0.01
Sun 04/05 02Z 0.04 1731  94  82   7 0.01
Sun 04/05 03Z 0.04 1733  96  82   7 0.01
Sun 04/05 04Z 0.05 1736  97  88   8 0.01
Sun 04/05 05Z 0.05 1740  97  90   8 0.02
Sun 04/05 06Z 0.07 1742  97  83   8 0.03
Sun 04/05 07Z 0.10 1742  97  85   9 0.02
Sun 04/05 08Z 0.13 1840  97  85   9 0.03
Sun 04/05 09Z 0.19 1839  98  74   9 0.03
Sun 04/05 10Z 0.25 1939  98  64  10 0.04
Sun 04/05 11Z 0.36 2038  98  69   8 0.04
Sun 04/05 12Z 0.46 2233  98  92   7 0.12
Sun 04/05 13Z 0.48 2329  98  98   7 0.08
Sun 04/05 14Z 0.50 2328  97  91   7 0.07
Sun 04/05 15Z 0.57 2427  96  73   5 0.03
Sun 04/05 16Z 0.64 2526  96  70   3 0.02
Sun 04/05 17Z 0.74 2525  95  38   2 0.01
Sun 04/05 18Z 0.82 2524  93  22   0 0.01
Sun 04/05 19Z 1.09 2524  95  19   0 0.01
Sun 04/05 20Z 1.61 2622  94  23  -1 0.01
Sun 04/05 21Z 2.56 2622  91  20  -2 0.01
Sun 04/05 22Z 2.43 2624  90  21  -2 0.00
Sun 04/05 23Z 2.37 2627  92  19  -3 0.00
Mon 04/06 00Z 1.97 2629  93  20  -5 0.00
Mon 04/06 01Z 1.87 2730  91  24  -5 0.00
Mon 04/06 02Z 1.88 2729  92  28  -6 0.00
Mon 04/06 03Z 1.61 2730  94  36  -7 0.00
Mon 04/06 04Z 1.58 2731  95  38  -7 0.00
Mon 04/06 05Z 1.65 2732  96  46  -8 0.01
Mon 04/06 06Z 1.50 2832  95  55  -8 0.00
Mon 04/06 07Z 1.30 2832  96  59  -8 0.00
Mon 04/06 08Z 1.28 2831  96  50  -8 0.00
Mon 04/06 09Z 1.48 2831  96  42  -8 0.00
Mon 04/06 10Z 1.48 2930  97  39  -9 0.00
Mon 04/06 11Z 1.33 2928  96  43  -9 0.00
Mon 04/06 12Z 1.42 2926  97  51  -9 0.00
Mon 04/06 13Z 1.69 2823  97  57  -9 0.00
Mon 04/06 14Z 1.89 2822  96  68  -9 0.00
Mon 04/06 15Z 4.59 2821  94  72  -9 0.00
Mon 04/06 16Z 6.77 2821  91  73  -9 0.00
Mon 04/06 17Z 8.88 2720  87  73  -9 0.00
Mon 04/06 18Z 11.26 2720  84  71  -8 0.00
Mon 04/06 19Z 8.96 2719  83  76  -8 0.00
Mon 04/06 20Z 6.45 2719  86  79  -8 0.00
Mon 04/06 21Z 5.87 2719  85  80  -8 0.00
Mon 04/06 22Z 3.53 2819  84  79  -8 0.00
Mon 04/06 23Z 1.64 2818  89  80  -8 0.00

Run total areal avg QPF for the Central_Greens is: 0.66 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