NAM3 EXPERIMENTAL Froude Number for the Central Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the Central_Greens

Model run: BTV_GRID_D2D_NAM3_20260827_0600
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 08/27 06Z 0.20 1911  80  18  11 0.00
Thu 08/27 07Z 0.31 2013  76  18  12 0.00
Thu 08/27 08Z 0.44 2017  73  20  12 0.00
Thu 08/27 09Z 0.53 2020  70  18  12 0.00
Thu 08/27 10Z 0.53 2022  68  22  12 0.00
Thu 08/27 11Z 0.54 2022  60  32  13 0.00
Thu 08/27 12Z 0.59 2123  56  31  13 0.00
Thu 08/27 13Z 0.61 2124  58  38  13 0.00
Thu 08/27 14Z 0.64 2123  69  44  13 0.00
Thu 08/27 15Z 0.71 2022  72  44  13 0.00
Thu 08/27 16Z 2.07 2021  80  38  13 0.00
Thu 08/27 17Z 1.82 2021  85  63  13 0.00
Thu 08/27 18Z 0.76 2021  92  86  13 0.01
Thu 08/27 19Z 0.56 2021  93  89  13 0.02
Thu 08/27 20Z 0.52 1920  94  86  14 0.01
Thu 08/27 21Z 0.48 1922  96  81  14 0.05
Thu 08/27 22Z 0.36 1924  95  80  14 0.06
Thu 08/27 23Z 0.50 2024  90  79  14 0.40
Fri 08/28 00Z 0.56 2026  91  81  13 0.27
Fri 08/28 01Z 0.58 2127  92  78  14 0.02
Fri 08/28 02Z 0.58 2126  82  71  14 0.05
Fri 08/28 03Z 0.64 2226  85  74  14 0.03
Fri 08/28 04Z 0.66 2326  87  67  14 0.02
Fri 08/28 05Z 0.64 2424  87  66  14 0.01
Fri 08/28 06Z 0.62 2522  92  58  14 0.01
Fri 08/28 07Z 0.56 2519  93  56  13 0.01
Fri 08/28 08Z 0.48 2616  91  61  13 0.01
Fri 08/28 09Z 0.39 2614  88  54  13 0.01
Fri 08/28 10Z 0.34 2612  88  63  13 0.00
Fri 08/28 11Z 0.29 2610  87  52  12 0.00
Fri 08/28 12Z 0.30 2611  88  42  12 0.00
Fri 08/28 13Z 0.30 2610  89  53  12 0.00
Fri 08/28 14Z 0.27 2609  90  50  12 0.00
Fri 08/28 15Z 0.26 2608  91  45  12 0.00
Fri 08/28 16Z 0.27 2608  91  28  12 0.00
Fri 08/28 17Z 0.31 2608  91  19  12 0.00
Fri 08/28 18Z 0.36 2608  90   9  12 0.00
Fri 08/28 19Z 0.38 2709  92   4  11 0.00
Fri 08/28 20Z 0.33 2809  93   5  11 0.01
Fri 08/28 21Z 0.27 2808  91   8  12 0.00
Fri 08/28 22Z 0.26 2908  93   9  11 0.01
Fri 08/28 23Z 0.25 2909  92  11  11 0.01
Sat 08/29 00Z 0.25 3010  92  15  11 0.00
Sat 08/29 01Z 0.23 3011  92  19  10 0.00
Sat 08/29 02Z 0.19 3110  91  21  10 0.00
Sat 08/29 03Z 0.17 3110  87  22  10 0.00
Sat 08/29 04Z 0.17 3111  81  26  10 0.00
Sat 08/29 05Z 0.16 3111  74  26  10 0.00
Sat 08/29 06Z 0.17 3111  67  20  10 0.00
Sat 08/29 07Z 0.16 3112  58  17  10 0.00
Sat 08/29 08Z 0.15 3112  51  14   9 0.00
Sat 08/29 09Z 0.14 3212  48  15   9 0.00
Sat 08/29 10Z 0.12 3212  46  12   9 0.00
Sat 08/29 11Z 0.10 3211  45  10   9 0.00
Sat 08/29 12Z 0.09 3210  45   6   9 0.00
Sat 08/29 13Z 0.09 3210  47   5   8 0.00
Sat 08/29 14Z 0.12 3209  51   5   8 0.00
Sat 08/29 15Z 0.15 3108  54   5   8 0.00
Sat 08/29 16Z 0.16 3006  58   5   8 0.00
Sat 08/29 17Z 0.28 2906  58   4   8 0.00

Run total areal avg QPF for the Central_Greens is: 1.02 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