Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260402_1800
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)
=== ===== === ==== ==== === === === ====
Thu 04/02 18Z 0.08 1409  99  84   0 0.00
Thu 04/02 19Z 0.10 1412  97  91   0 0.00
Thu 04/02 20Z 0.11 1414  96  90   1 0.00
Thu 04/02 21Z 0.10 1416  95  86   1 0.00
Thu 04/02 22Z 0.08 1517  95  97   1 0.00
Thu 04/02 23Z 0.08 1520  95  99   1 0.01
Fri 04/03 00Z 0.05 1623  96  97   2 0.02
Fri 04/03 02Z 0.03 1725  97  88   3 0.02
Fri 04/03 03Z 0.07 1727  97  87   4 0.02
Fri 04/03 04Z 0.10 1828  98  86   4 0.02
Fri 04/03 05Z 0.15 1830  98  88   5 0.03
Fri 04/03 06Z 0.18 1930  97  79   7 0.03
Fri 04/03 07Z 0.24 1932  98  69   7 0.04
Fri 04/03 08Z 0.25 2032  97  73   9 0.03
Fri 04/03 09Z 0.29 2033  98  89   9 0.02
Fri 04/03 10Z 0.36 2136  98  87  10 0.04
Fri 04/03 11Z 0.40 2137  98  90  10 0.04
Fri 04/03 12Z 0.45 2239  98  90  11 0.04
Fri 04/03 13Z 0.47 2237  97  88  11 0.07
Fri 04/03 14Z 0.51 2338  98  88  11 0.05
Fri 04/03 15Z 0.58 2338  98  94  11 0.05
Fri 04/03 16Z 0.64 2438  96  75  11 0.03
Fri 04/03 17Z 0.66 2437  94  76  11 0.02
Fri 04/03 18Z 0.72 2537  95  85  11 0.01
Fri 04/03 19Z 0.76 2537  95  84  11 0.01
Fri 04/03 20Z 0.83 2537  95  51  11 0.02
Fri 04/03 21Z 0.93 2537  94  43  11 0.00
Fri 04/03 22Z 1.05 2538  93  57  10 0.00
Fri 04/03 23Z 1.13 2540  95  34  10 0.00
Sat 04/04 00Z 1.23 2541  96  24  10 0.01
Sat 04/04 01Z 1.30 2544  95  15   9 0.01
Sat 04/04 02Z 1.27 2642  93  12   9 0.01
Sat 04/04 03Z 1.32 2641  92  11   8 0.02
Sat 04/04 04Z 1.23 2739  88  13   7 0.02
Sat 04/04 05Z 0.99 2736  84  25   6 0.02
Sat 04/04 06Z 0.75 2834  81  41   6 0.02
Sat 04/04 07Z 0.56 2830  81  32   5 0.00
Sat 04/04 08Z 0.42 2926  83  18   3 0.00
Sat 04/04 09Z 0.30 3023  86  20   2 0.00
Sat 04/04 10Z 0.19 3120  86  15   2 0.00
Sat 04/04 11Z 0.11 3217  86  20   2 0.00
Sat 04/04 12Z 0.05 3414  86  21   2 0.00
Sat 04/04 13Z 0.05 3510  86  28   2 0.00
Sat 04/04 14Z 0.07 0206  86  33   3 0.00
Sat 04/04 15Z 0.09 0704  87  54   3 0.00
Sat 04/04 16Z 0.10 1106  89  45   2 0.00
Sat 04/04 17Z 0.10 1308  86  46   3 0.00
Sat 04/04 18Z 0.11 1410  85  62   3 0.00
Sat 04/04 19Z 0.13 1513  84  49   3 0.00
Sat 04/04 20Z 0.15 1517  84  31   3 0.00
Sat 04/04 21Z 0.12 1520  84  40   4 0.00
Sat 04/04 22Z 0.05 1621  82  97   5 0.00
Sat 04/04 23Z 0.04 1623  82  97   5 0.00
Sun 04/05 00Z 0.05 1624  85  93   5 0.01
Sun 04/05 01Z 0.05 1626  86  93   6 0.01
Sun 04/05 02Z 0.04 1728  90  94   6 0.00
Sun 04/05 03Z 0.04 1730  93  79   7 0.00
Sun 04/05 04Z 0.07 1732  95  87   7 0.00
Sun 04/05 05Z 0.08 1734  96  94   8 0.01

Run total areal avg QPF for the Central_Greens is: 0.76 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