Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260617_1200
Using the MB925 to MB850 layer.
Assumes greens are orthogonal to 270 degree winds.

925-850 mb Layer Average Wind/RH. Avg QPF over the greens.
Date   Time        Wind RH% 700 850T QPF
Day mm/dd hhZ Frd# DDFF (%) RH% (C) (in)
=== ===== === ==== ==== === === === ====
Wed 06/17 12Z 0.21 2010  72  77   9 0.00
Wed 06/17 13Z 0.26 2010  68  69   9 0.00
Wed 06/17 14Z 1.00 2010  65  60   9 0.00
Wed 06/17 15Z 2.15 2008  62  54  10 0.00
Wed 06/17 16Z 2.09 2008  58  42  10 0.01
Wed 06/17 17Z 0.88 1907  57  37  10 0.01
Wed 06/17 18Z 0.77 1808  56  40  11 0.00
Wed 06/17 19Z 0.92 1809  54  53  11 0.00
Wed 06/17 20Z 0.68 1808  55  69  11 0.00
Wed 06/17 21Z 0.40 1708  58  74  11 0.00
Wed 06/17 22Z 0.31 1710  61  77  11 0.00
Wed 06/17 23Z 0.12 1714  65  84  11 0.00
Thu 06/18 00Z 0.12 1816  68  72  11 0.00
Thu 06/18 01Z 0.13 1818  69  46  11 0.00
Thu 06/18 02Z 0.32 1922  73  48  11 0.00
Thu 06/18 03Z 0.38 1924  81  61  11 0.00
Thu 06/18 04Z 0.25 1924  84  63  11 0.01
Thu 06/18 05Z 0.27 1924  86  71  11 0.00
Thu 06/18 06Z 0.29 2023  87  52  11 0.00
Thu 06/18 07Z 0.29 2022  88  69  11 0.00
Thu 06/18 08Z 0.31 2021  89  90  11 0.03
Thu 06/18 09Z 0.11 1820  88  91  11 0.02
Thu 06/18 10Z 0.10 1725  85  96  11 0.01
Thu 06/18 11Z 0.12 1732  82  96  12 0.01
Thu 06/18 12Z 0.07 1737  87  91  13 0.01
Thu 06/18 13Z 0.18 1842  92  93  12 0.02
Thu 06/18 14Z 0.08 1841  86  90  13 0.05
Thu 06/18 15Z 0.12 1840  96  94  13 0.17
Thu 06/18 16Z 0.14 1836  98  80  13 0.18
Thu 06/18 17Z 0.26 1934  97  71  13 0.06
Thu 06/18 18Z 0.36 1932  96  55  13 0.02
Thu 06/18 19Z 0.56 2030  94  59  14 0.01
Thu 06/18 20Z 1.89 2126  91  65  13 0.01
Thu 06/18 21Z 2.16 2325  90  52  13 0.07
Thu 06/18 22Z 1.33 2424  95  57  13 0.03
Thu 06/18 23Z 1.61 2528  88  63  12 0.06
Fri 06/19 00Z 1.47 2527  84  73  11 0.02
Fri 06/19 01Z 1.44 2528  84  60  10 0.01
Fri 06/19 02Z 1.31 2529  86  63   9 0.00
Fri 06/19 03Z 1.12 2529  89  63   9 0.00
Fri 06/19 04Z 1.03 2629  88  63   9 0.00
Fri 06/19 05Z 1.11 2630  91  75   8 0.00
Fri 06/19 06Z 1.09 2630  93  68   8 0.01
Fri 06/19 07Z 1.06 2630  94  66   8 0.01
Fri 06/19 08Z 0.91 2629  94  67   8 0.01
Fri 06/19 09Z 0.89 2631  94  70   9 0.01
Fri 06/19 10Z 0.93 2633  94  62   9 0.01
Fri 06/19 11Z 0.92 2733  93  50   9 0.01
Fri 06/19 12Z 0.97 2733  92  45   9 0.01
Fri 06/19 13Z 1.04 2732  92  41   9 0.01
Fri 06/19 14Z 1.20 2731  92  42   9 0.01
Fri 06/19 15Z 1.50 2729  90  46   9 0.01
Fri 06/19 16Z 2.55 2727  89  52   9 0.00
Fri 06/19 17Z 7.29 2625  87  53   9 0.00
Fri 06/19 18Z 10.15 2623  87  52   9 0.00
Fri 06/19 19Z 11.81 2623  85  47  10 0.00
Fri 06/19 20Z 12.53 2624  83  40  10 0.00
Fri 06/19 21Z 13.23 2625  79  38  10 0.00
Fri 06/19 22Z 11.02 2627  70  35  10 0.03
Fri 06/19 23Z 6.11 2629  75  41  10 0.01

Run total areal avg QPF for the greens is: 0.96 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