Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260618_0000
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 06/18 00Z 0.46 2012  68  93  11 0.00
Thu 06/18 01Z 0.53 1914  71  97  11 0.00
Thu 06/18 02Z 0.54 2017  83  93  11 0.04
Thu 06/18 03Z 0.63 2120  80  89  11 0.05
Thu 06/18 04Z 0.65 2122  82  92  11 0.00
Thu 06/18 05Z 0.52 2021  85  89  11 0.00
Thu 06/18 06Z 0.40 2020  89  82  11 0.02
Thu 06/18 07Z 0.33 2020  89  76  12 0.00
Thu 06/18 08Z 0.44 2023  92  95  11 0.03
Thu 06/18 09Z 0.41 2021  95  96  11 0.19
Thu 06/18 10Z 0.39 2022  96  93  11 0.19
Thu 06/18 11Z 0.26 1923  92  86  12 0.05
Thu 06/18 12Z 0.33 1928  90  95  12 0.02
Thu 06/18 13Z 0.33 1935  92  97  12 0.05
Thu 06/18 14Z 0.41 1937  92  91  12 0.04
Thu 06/18 15Z 0.41 1937  92  83  12 0.02
Thu 06/18 16Z 0.47 1939  97  84  12 0.08
Thu 06/18 17Z 0.22 1833  94  54  14 0.06
Thu 06/18 18Z 0.40 1931  94  55  14 0.01
Thu 06/18 19Z 0.62 1928  95  75  13 0.01
Thu 06/18 20Z 0.82 2026  94  46  14 0.01
Thu 06/18 21Z 0.90 2324  95  76  13 0.13
Thu 06/18 22Z 1.00 2525  87  49  13 0.15
Thu 06/18 23Z 1.21 2524  94  62  12 0.00
Fri 06/19 00Z 1.51 2427  90  46  12 0.01
Fri 06/19 01Z 2.06 2531  87  69  11 0.01
Fri 06/19 02Z 1.66 2532  93  47  10 0.02
Fri 06/19 03Z 1.45 2531  93  56   9 0.01
Fri 06/19 04Z 1.20 2531  94  72   9 0.01
Fri 06/19 05Z 1.12 2630  96  75   9 0.03
Fri 06/19 06Z 1.09 2631  96  67   8 0.01
Fri 06/19 07Z 0.99 2631  95  70   8 0.01
Fri 06/19 08Z 0.91 2630  96  72   9 0.01
Fri 06/19 09Z 0.89 2730  96  71   8 0.01
Fri 06/19 10Z 0.84 2729  96  69   8 0.01
Fri 06/19 11Z 0.80 2728  96  70   8 0.01
Fri 06/19 12Z 0.80 2728  96  68   8 0.01
Fri 06/19 13Z 0.81 2727  92  65   8 0.01
Fri 06/19 14Z 0.87 2726  89  61   9 0.00
Fri 06/19 15Z 1.21 2625  91  63   9 0.00
Fri 06/19 16Z 4.59 2623  91  61   9 0.00
Fri 06/19 17Z 11.03 2621  87  61   9 0.00
Fri 06/19 18Z 10.22 2521  87  59  10 0.00
Fri 06/19 19Z 11.62 2621  83  55  10 0.00
Fri 06/19 20Z 12.77 2621  83  57  10 0.00
Fri 06/19 21Z 11.63 2521  81  43  10 0.00
Fri 06/19 22Z 8.76 2523  79  35  10 0.00
Fri 06/19 23Z 4.32 2525  73  41  10 0.00
Sat 06/20 00Z 2.45 2528  73  36  10 0.00
Sat 06/20 01Z 2.24 2531  80  41   9 0.00
Sat 06/20 02Z 1.74 2632  87  49   9 0.01
Sat 06/20 03Z 1.28 2831  90  58   8 0.04
Sat 06/20 04Z 1.01 2829  90  63   8 0.03
Sat 06/20 05Z 0.95 2828  93  71   7 0.02
Sat 06/20 06Z 0.96 2728  95  84   7 0.02
Sat 06/20 07Z 0.95 2728  95  85   7 0.03
Sat 06/20 08Z 0.94 2729  95  84   7 0.01
Sat 06/20 09Z 0.97 2731  95  86   7 0.02
Sat 06/20 10Z 1.01 2733  97  91   7 0.05
Sat 06/20 11Z 1.04 2832  97  90   6 0.04

Run total areal avg QPF for the Central_Greens is: 1.59 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