NAM3 EXPERIMENTAL Froude Number for the Green Mountains

Subject: NAM3 EXPERIMENTAL Froude Number for the greens

Model run: BTV_GRID_D2D_NAM3_20260726_1800
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)
=== ===== === ==== ==== === === === ====
Sun 07/26 18Z 0.35 1600  81  51  13 0.00
Sun 07/26 19Z 0.51 1202  80  54  13 0.05
Sun 07/26 20Z 0.38 1303  80  54  13 0.06
Sun 07/26 21Z 0.24 1302  79  49  14 0.02
Sun 07/26 22Z 0.24 1403  80  47  14 0.01
Sun 07/26 23Z 0.15 1504  83  48  13 0.00
Mon 07/27 00Z 0.12 1606  86  50  13 0.01
Mon 07/27 01Z 0.07 1707  87  51  13 0.02
Mon 07/27 02Z 0.05 1708  87  46  13 0.00
Mon 07/27 03Z 0.05 1809  87  40  13 0.00
Mon 07/27 04Z 0.10 1908  85  38  13 0.00
Mon 07/27 05Z 0.15 2007  84  39  13 0.00
Mon 07/27 06Z 0.20 2206  82  37  13 0.00
Mon 07/27 07Z 0.22 2306  82  39  13 0.00
Mon 07/27 08Z 0.25 2506  84  43  13 0.00
Mon 07/27 09Z 0.24 2406  87  48  12 0.00
Mon 07/27 10Z 0.19 2305  90  53  12 0.00
Mon 07/27 11Z 0.16 2205  91  59  12 0.00
Mon 07/27 12Z 0.15 2205  93  69  12 0.00
Mon 07/27 13Z 0.14 2105  94  73  12 0.01
Mon 07/27 14Z 0.13 2205  94  76  12 0.01
Mon 07/27 15Z 0.18 2305  94  76  12 0.01
Mon 07/27 16Z 0.09 2003  92  73  12 0.00
Mon 07/27 17Z 0.13 1903  90  71  12 0.00
Mon 07/27 18Z 0.30 2004  89  70  13 0.00
Mon 07/27 19Z 0.37 2005  87  62  13 0.01
Mon 07/27 20Z 0.50 2105  87  62  13 0.00
Mon 07/27 21Z 0.42 2105  87  65  14 0.00
Mon 07/27 22Z 0.21 2005  87  66  14 0.00
Mon 07/27 23Z 0.16 2006  88  63  14 0.00
Tue 07/28 00Z 0.27 2108  88  63  14 0.00
Tue 07/28 01Z 0.33 2109  89  63  13 0.00
Tue 07/28 02Z 0.33 2111  90  69  13 0.00
Tue 07/28 03Z 0.28 2012  89  67  13 0.00
Tue 07/28 04Z 0.29 2013  89  60  13 0.00
Tue 07/28 05Z 0.29 2014  90  57  13 0.00
Tue 07/28 06Z 0.24 2014  91  58  13 0.00
Tue 07/28 07Z 0.31 2116  91  67  13 0.00
Tue 07/28 08Z 0.29 2115  88  71  13 0.00
Tue 07/28 09Z 0.10 1912  84  63  14 0.00
Tue 07/28 10Z 0.03 1713  82  59  14 0.00
Tue 07/28 11Z 0.07 1815  88  67  13 0.00
Tue 07/28 12Z 0.05 1814  90  69  13 0.00
Tue 07/28 13Z 0.03 1714  91  69  13 0.00
Tue 07/28 14Z 0.08 1715  92  73  13 0.00
Tue 07/28 15Z 0.13 1615  93  75  13 0.01
Tue 07/28 16Z 0.27 1616  94  75  13 0.00
Tue 07/28 17Z 0.30 1716  94  74  13 0.00
Tue 07/28 18Z 0.34 1616  94  67  14 0.00
Tue 07/28 19Z 0.22 1617  94  67  14 0.01
Tue 07/28 20Z 0.19 1618  95  71  14 0.02
Tue 07/28 21Z 0.14 1617  94  72  14 0.07
Tue 07/28 22Z 0.20 1619  94  69  14 0.04
Tue 07/28 23Z 0.22 1620  96  71  14 0.02
Wed 07/29 00Z 0.26 1521  95  69  14 0.01
Wed 07/29 01Z 0.20 1622  96  70  14 0.01
Wed 07/29 02Z 0.16 1623  96  69  13 0.01
Wed 07/29 03Z 0.13 1621  95  63  13 0.01
Wed 07/29 04Z 0.15 1621  92  57  13 0.01
Wed 07/29 05Z 0.13 1619  88  56  13 0.00

Run total areal avg QPF for the greens is: 0.43 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