Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260314_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)
=== ===== === ==== ==== === === === ====
Sat 03/14 18Z 2.92 2524  96  83  -7 0.00
Sat 03/14 19Z 5.66 2729  91  80  -7 0.03
Sat 03/14 20Z 10.29 2831  83  76  -8 0.01
Sat 03/14 21Z 5.54 2834  87  74  -9 0.01
Sat 03/14 22Z 3.76 2835  89  73 -10 0.01
Sat 03/14 23Z 1.67 2933  92  69 -10 0.01
Sun 03/15 00Z 1.50 2931  95  54 -10 0.01
Sun 03/15 01Z 1.47 2930  95  43 -11 0.01
Sun 03/15 02Z 1.22 3027  94  20 -11 0.01
Sun 03/15 03Z 1.20 3026  93   9 -11 0.01
Sun 03/15 04Z 0.86 3024  88  10 -12 0.00
Sun 03/15 05Z 0.56 3124  77   7 -11 0.00
Sun 03/15 06Z 0.43 3123  66   9 -10 0.00
Sun 03/15 07Z 0.34 3121  55  14  -9 0.00
Sun 03/15 08Z 0.28 3119  47  11  -8 0.00
Sun 03/15 09Z 0.23 3117  41  14  -8 0.00
Sun 03/15 10Z 0.16 3216  30  18  -7 0.00
Sun 03/15 11Z 0.11 3213  23  21  -7 0.00
Sun 03/15 12Z 0.06 3310  20  32  -7 0.00
Sun 03/15 13Z 0.06 3105  22  71  -7 0.00
Sun 03/15 14Z 0.05 2402  24  91  -7 0.00
Sun 03/15 15Z 0.02 1703  25  94  -7 0.00
Sun 03/15 16Z 0.04 1508  28  98  -7 0.00
Sun 03/15 17Z 0.07 1613  38  98  -7 0.00
Sun 03/15 18Z 0.07 1618  55  98  -7 0.00
Sun 03/15 19Z 0.03 1621  61  98  -6 0.00
Sun 03/15 20Z 0.05 1625  61  98  -5 0.00
Sun 03/15 21Z 0.06 1630  51  98  -4 0.00
Sun 03/15 22Z 0.04 1733  37  94  -2 0.00
Sun 03/15 23Z 0.10 1736  34  71  -1 0.00
Mon 03/16 00Z 0.15 1839  34  48   0 0.00
Mon 03/16 01Z 0.19 1842  29  53   0 0.00
Mon 03/16 02Z 0.20 1844  25  64   1 0.00
Mon 03/16 03Z 0.20 1846  25  72   2 0.00
Mon 03/16 04Z 0.19 1848  28  72   2 0.00
Mon 03/16 05Z 0.17 1848  55  51   3 0.00
Mon 03/16 06Z 0.13 1748  72  49   3 0.00
Mon 03/16 07Z 0.09 1748  87  56   3 0.01
Mon 03/16 08Z 0.05 1748  90  73   4 0.01
Mon 03/16 09Z 0.06 1649  94  71   6 0.02
Mon 03/16 10Z 0.11 1650  95  92   7 0.04
Mon 03/16 11Z 0.10 1651  95  98   7 0.14
Mon 03/16 12Z 0.03 1649  96  91   7 0.11
Mon 03/16 13Z 0.13 1746  97  46   8 0.03
Mon 03/16 14Z 0.22 1846  98  31   9 0.02
Mon 03/16 15Z 0.33 1945  98  19   9 0.02
Mon 03/16 16Z 0.37 1945  97  24   9 0.01
Mon 03/16 17Z 0.43 1944  95  23   9 0.01
Mon 03/16 18Z 0.46 1943  94  22  10 0.00
Mon 03/16 19Z 0.40 1942  95  31  10 0.00
Mon 03/16 20Z 0.34 1844  95  39  10 0.00
Mon 03/16 21Z 0.33 1846  95  68  10 0.00
Mon 03/16 22Z 0.29 1846  96  58  10 0.01
Mon 03/16 23Z 0.28 1847  96  48  10 0.01
Tue 03/17 00Z 0.33 1847  96  59   9 0.01
Tue 03/17 01Z 0.26 1842  96  84   9 0.01
Tue 03/17 02Z 0.27 1827  99  96   8 0.10
Tue 03/17 03Z 0.13 1730  97  92   8 0.12
Tue 03/17 04Z 0.21 1828  99  95   7 0.05
Tue 03/17 05Z 0.53 2621  97  96   0 0.10

Run total areal avg QPF for the Central_Greens is: 0.94 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